Weird output after submit

On this page, the users are randomly getting a response like this after submit (see screendump as well, if you do not want to click the link).
Today this was from Mac / Chrome.., however not related to that combo only:
https://www.smvsilkeborg.dk/begivenhed/lotterispil-2/?instance_id=1954&callback=jQuery200106038985626826323_1697802210409&request_type=jsonp&ai1ec_doing_ajax=true&ai1ec&_=1697802210411#wpcf7-f1623-o1

Image here: https://www.dropbox.com/scl/fi/zvb06lciqrcxd0ibvnn9l/Sk-rmbillede-2023-10-20-kl.-13.55.22.png?rlkey=9c16icxfr6htxg0zeqfoy8x2t&dl=0

What can be the issue here..?

Best,
Morten

• This topic was modified 1 year, 5 months ago by Morten.
• This topic was modified 1 year, 5 months ago by Morten.

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