Suddenly form does not submit all fields

[GASOLINE]

My client still works with Joomla 3.10.11 and Mosets 3.10.12.
In a couple of months we will upgrade to Joomla 4 and the new Mosets. But for now he has issue that with a complicated form everything seems to work but after sending there is an error and only half off the form is filled in.
Nothing has changed on the website, and the VPS is still running PHP 7.4.33

A client can than login again on site and change his form and then everything is filled in.

Any idea how to solve this??

The error it gave is: "0 - timeout-or-duplicate"



The form (after field WEBSITE everything is missing except consent).