Submitting form returns 502 and never-ending load animation

Hi experts,

My form built with CF7 + Conditional Fields works fine for the first submit. However, after the 2nd submit with the same browser, the loading animation never stops and the request returns 502.

I already tried theme/plugins deactivation and determined that it’s only reproduced with Conditional Fields. CF7 itself works super fine. Already posted a thread at appropriate place, though no progress so far.

I dared to create this topic here knowing it might be off-topic, because I am expecting much more exposure. Only if you have any idea about this, a piece of comment would be greatly appreciated!!

Thanks,
Mayumi

In case it helps, here’s the request headers;

Request URL: https://fida-staging.work/wp-json/contact-form-7/v1/contact-forms/2670/feedback?_locale=user
Request Method: POST
Status Code: 502 
Remote Address: 150.95.219.91:443
Referrer Policy: strict-origin-when-cross-origin
content-length: 494
content-type: text/html
date: Tue, 02 Mar 2021 01:14:02 GMT
etag: "5e717190-1ee"
server: nginx
:authority: fida-staging.work
:method: POST
:path: /wp-json/contact-form-7/v1/contact-forms/2670/feedback?_locale=user
:scheme: https
accept: application/json, */*;q=0.1
accept-encoding: gzip, deflate, br
accept-language: ja
content-length: 8117
content-type: multipart/form-data; boundary=----WebKitFormBoundaryOTEw0EziIK41mb3b
cookie: PHPSESSID=ee3fbdf0e5b15ea4755de5c53850e811; cf7msm_big_cookie=0; cf7msm_posted_data=%7B%22biztype%22%3A%5B%22%E9%85%AA%E8%BE%B2%22%5D%2C%22dairy-type%22%3A%5B%22%E3%83%9B%E3%83%AB%E3%82%B9%E3%82%BF%E3%82%A4%E3%83%B3%22%5D%2C%22dairy-type-other%22%3A%22%22%2C%22cowhouse%22%3A%5B%22%E3%81%A4%E3%81%AA%E3%81%8E%22%5D%2C%22milk-quantity%22%3A%2230%22%2C%22dairy-concern%22%3A%5B%22%E4%B9%B3%E9%87%8F%E3%81%8C%E4%BD%8E%E3%81%84%22%5D%2C%22viable-bacteria%22%3A%22%22%2C%22cells%22%3A%22%22%2C%22fat%22%3A%22%22%2C%22protein%22%3A%22%22%2C%22dairy-concern-textarea%22%3A%22%22%2C%22month%22%3A%22%22%2C%22weight%22%3A%22%22%2C%22meat-concern-textarea%22%3A%22%22%2C%22pig-month%22%3A%22%22%2C%22fc%22%3A%22%22%2C%22pig-concern-textarea%22%3A%22%22%2C%22layer-concern-textarea%22%3A%22%22%2C%22other-animal%22%3A%22%22%2C%22disease%22%3A%5B%22%E4%B8%8B%E7%97%A2%EF%BC%88%E6%84%9F%E6%9F%93%E6%80%A7%EF%BC%89%22%5D%2C%22other-disease%22%3A%22%22%2C%22feed-concern%22%3A%5B%22%E5%8F%8E%E9%87%8F%E3%81%8C%E4%BD%8E%E3%81%84%22%5D%2C%22feed-concern-other%22%3A%22%22%2C%22poop%22%3A%5B%22%E7%95%9C%E8%88%8E%E3%81%AE%E6%82%AA%E8%87%AD%22%5D%2C%22poop-other%22%3A%22%22%2C%22nums%22%3A%22500%22%2C%22meat-pattern%22%3A%5B%22%22%5D%2C%22meat-type%22%3A%5B%22%22%5D%2C%22meat-house%22%3A%5B%22%22%5D%2C%22meat-concern%22%3A%5B%22%22%5D%2C%22pig-type%22%3A%5B%22%22%5D%2C%22pig-concern%22%3A%5B%22%22%5D%2C%22chicken-type%22%3A%5B%22%22%5D%2C%22chicken-nurture-type%22%3A%5B%22%22%5D%2C%22chicken-house%22%3A%5B%22%22%5D%2C%22concern-broiler%22%3A%5B%22%22%5D%2C%22allin-allout%22%3A%5B%22%22%5D%2C%22layer-concern%22%3A%5B%22%22%5D%2C%22multistep-1%22%3A%22%22%7D
origin: https://fida-staging.work
referer: https://fida-staging.work/shindan-test/
sec-ch-ua: "Chromium";v="88", "Google Chrome";v="88", ";Not A Brand";v="99"
sec-ch-ua-mobile: ?0
sec-fetch-dest: empty
sec-fetch-mode: cors
sec-fetch-site: same-origin
user-agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 11_2_2) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/88.0.4324.192 Safari/537.36
x-wp-nonce: 7bce1c6ec6
_locale: user
_wpcf7: 2670
_wpcf7_version: 5.4
_wpcf7_locale: en_US
_wpcf7_unit_tag: wpcf7-f2670-p2650-o1
_wpcf7_container_post: 2650
_wpcf7_posted_data_hash: 
_wpcf7cf_hidden_group_fields: ["dairy-type[]","dairy-type[]","dairy-type[]","dairy-type-other","cowhouse","cowhouse","cowhouse","milk-quantity","dairy-concern[]","dairy-concern[]","dairy-concern[]","dairy-concern[]","viable-bacteria","cells","fat","protein","dairy-concern-textarea","dairy-type-other","viable-bacteria","cells","fat","protein","dairy-concern-textarea","meat-pattern","meat-pattern","meat-type","meat-type","meat-type","meat-type","meat-house","meat-house","month","weight","meat-concern[]","meat-concern[]","meat-concern[]","meat-concern[]","meat-concern[]","meat-concern-textarea","meat-concern-textarea","pig-concern-textarea","chicken-type","chicken-type","chicken-type","chicken-nurture-type","chicken-nurture-type","chicken-nurture-type","chicken-house","chicken-house","concern-broiler[]","concern-broiler[]","concern-broiler[]","layer-concern-textarea","allin-allout","allin-allout","layer-concern[]","layer-concern[]","layer-concern[]","layer-concern[]","layer-concern-textarea","concern-broiler[]","concern-broiler[]","concern-broiler[]","layer-concern-textarea","layer-concern-textarea","allin-allout","allin-allout","layer-concern[]","layer-concern[]","layer-concern[]","layer-concern[]","layer-concern-textarea","layer-concern-textarea","other-animal","other-disease","feed-concern-other","poop-other"]
_wpcf7cf_hidden_groups: ["dairy-group","dairy-type-other","group-dairy-quality","dairy-concern-other","meat","group-meat-concern","group-pig-concern","chicken","group-broiler","group-broiler-other","layer","group-layer-concern","group-other-animal","group-disease-other","feed-concern-other","poop-other"]
_wpcf7cf_visible_groups: ["pig"]
_wpcf7cf_repeaters: []
_wpcf7cf_steps: {}
_wpcf7cf_options: {"form_id":2670,"conditions":[{"then_field":"dairy-group","and_rules":[{"if_field":"biztype","operator":"equals","if_value":"\u916a\u8fb2"}]},{"then_field":"meat","and_rules":[{"if_field":"biztype","operator":"equals","if_value":"\u8089\u725b"}]},{"then_field":"pig","and_rules":[{"if_field":"biztype","operator":"equals","if_value":"\u990a\u8c5a"}]},{"then_field":"chicken","and_rules":[{"if_field":"biztype","operator":"equals","if_value":"\u990a\u9d8f"}]},{"then_field":"layer","and_rules":[{"if_field":"chicken-type","operator":"equals","if_value":"\u30ec\u30a4\u30e4\u30fc"}]},{"then_field":"dairy-concern-other","and_rules":[{"if_field":"dairy-concern","operator":"equals","if_value":"\u305d\u306e\u4ed6"}]},{"then_field":"group-meat-concern","and_rules":[{"if_field":"meat-concern","operator":"equals","if_value":"\u305d\u306e\u4ed6"}]},{"then_field":"group-pig-concern","and_rules":[{"if_field":"pig-concern","operator":"equals","if_value":"\u305d\u306e\u4ed6"}]},{"then_field":"group-layer-concern","and_rules":[{"if_field":"layer-concern","operator":"equals","if_value":"\u305d\u306e\u4ed6"}]},{"then_field":"group-other-animal","and_rules":[{"if_field":"biztype","operator":"equals","if_value":"\u305d\u306e\u4ed6"}]},{"then_field":"group-dairy-quality","and_rules":[{"if_field":"dairy-concern","operator":"equals","if_value":"\u4e73\u8cea\u304c\u60aa\u3044"}]},{"then_field":"dairy-type-other","and_rules":[{"if_field":"dairy-type","operator":"equals","if_value":"\u305d\u306e\u4ed6"}]},{"then_field":"group-broiler","and_rules":[{"if_field":"chicken-type","operator":"equals","if_value":"\u30d6\u30ed\u30a4\u30e9\u30fc"}]},{"then_field":"group-broiler","and_rules":[{"if_field":"chicken-type","operator":"equals","if_value":"\u5730\u9d8f"}]},{"then_field":"group-broiler-other","and_rules":[{"if_field":"concern-broiler","operator":"equals","if_value":"\u305d\u306e\u4ed6"}]},{"then_field":"group-disease-other","and_rules":[{"if_field":"disease","operator":"equals","if_value":"\u305d\u306e\u4ed6"}]},{"then_field":"group-disease-other","and_rules":[{"if_field":"disease","operator":"equals","if_value":"\u305d\u306e\u4ed6\u611f\u67d3\u75c7"}]},{"then_field":"feed-concern-other","and_rules":[{"if_field":"feed-concern","operator":"equals","if_value":"\u305d\u306e\u4ed6"}]},{"then_field":"poop-other","and_rules":[{"if_field":"poop","operator":"equals","if_value":"\u305d\u306e\u4ed6"}]}],"settings":{"animation":"yes","animation_intime":200,"animation_outtime":200,"conditions_ui":"normal","notice_dismissed":false}}
biztype: 養豚
dairy-type-other: 
milk-quantity: 
viable-bacteria: 
cells: 
fat: 
protein: 
dairy-concern-textarea: 
month: 
weight: 
meat-concern-textarea: 
pig-type: 肥育
pig-month: 10
fc: 10
pig-concern[]: 枝肉重量が低い
pig-concern-textarea: 
layer-concern-textarea: 
layer-concern-textarea: 
other-animal: 
disease[]: 下痢（感染性）
other-disease: 
feed-concern[]: 収量が低い
feed-concern-other: 
poop[]: 畜舎の悪臭
poop-other: 
nums: 500

The page I need help with: [log in to see the link]