Form loading continuously

Hi, I am having some troubles with one of our forms.

I try the form and it appears to work instantly. some users and some colleagues use the form and upon submitting the loading icon appears and nothing happens.

the error-log is bringing up the following:

jquery-migrate.min.js?ver=1.4.1:2 JQMIGRATE: Migrate is installed, version 1.4.1
api.optmnstr.com/v2/embed/49560/yhdyg3rqi9cpoppffmhh:1 Failed to load resource: the server responded with a status of 410 (Gone)
api.min.js:2 [OptinMonster] true
o.error @ api.min.js:2
(unknown) FullStory namespace conflict. Please set window[“_fs_namespace”].
VM462:1 leadsubmit cookie exists
/wp-json/contact-form-7/v1/contact-forms/1300/refill:1 Failed to load resource: the server responded with a status of 401 (Unauthorized)
VM504:2 Uncaught TypeError: Cannot read property ‘className’ of null
at <anonymous>:2:398
at gtm.js?id=GTM-WWVDM6Z:767
at Object.c [as __html] (gtm.js?id=GTM-WWVDM6Z:769)
at Ub (gtm.js?id=GTM-WWVDM6Z:659)
at h (gtm.js?id=GTM-WWVDM6Z:695)
at gtm.js?id=GTM-WWVDM6Z:639
at Array.<anonymous> (gtm.js?id=GTM-WWVDM6Z:697)
at Object.qf (gtm.js?id=GTM-WWVDM6Z:696)
at Md (gtm.js?id=GTM-WWVDM6Z:697)
at Od (gtm.js?id=GTM-WWVDM6Z:699)
at ve (gtm.js?id=GTM-WWVDM6Z:705)
at we (gtm.js?id=GTM-WWVDM6Z:704)
at xe (gtm.js?id=GTM-WWVDM6Z:707)
at Array.a.push (gtm.js?id=GTM-WWVDM6Z:709)
at ue (gtm.js?id=GTM-WWVDM6Z:704)
at Ug (gtm.js?id=GTM-WWVDM6Z:731)
at HTMLDocument.a (gtm.js?id=GTM-WWVDM6Z:741)
/wp-json/contact-form-7/v1/contact-forms/1300/feedback:1 Failed to load resource: the server responded with a status of 401 (Unauthorized)

Seems a bit strange that its only happening to some people though.

Any help appreciated.

Thanks