Error when adding Forms Designer: Sorry, something went wrong

[kloosterj]

I have a site collection with many subsites, on which we use Forms Designer on custom lists. This worked perfectly for about 100 subsites in the past years. Until some days ago, that is. Now, after clicking "Trust It" an error is thrown "Sorry, something went wrong. An unexpected error has occurred." On a different site collection things still work, so the issue seems limited to 1 site collection (and new subsites) only. As far as I know, nothing was changed in the settings. Scripting is still enabled. Existing subsites still work and the forms can still be edited and saved. Issue happens on all browsers.
Any idea what could be wrong, where to look and what to check?

[kloosterj]

The new Plumsail Forms seems to work correctly, so I will switch to using those.
Thanks

[linda.dillon]

I am having this same issue. Can you please explain in more detail what you say "The new Plumsail Forms seems to work correctly, so I will switch to using those."

[kloosterj]

Plumsail provides a new Forms product, which is also suitable for Modern. See https://plumsail.com/forms/store/sharepoint-forms/

[mnikitina]

Hello kloosterj,

Have you tried to add Forms Designer to a new subsite under different site collections? Do you get the same error?

Hello linda.dillon,

Have you checked that scripting capabilities are enabled for the Site Collection and for this specific site?

Do you get the same error on a different site?

And yes, Plumsail Forms is our newer product for Modern UI, and it supports only versions of SharePoint that come with Modern UI: SharePoint Online and 2019.