Can you try to enable the Joomla error reporting to maximum from the backend global configuration page and see what error it show on the composer page?

If it doesn't show any error, can you update your site backend and FTP access at https://stackideas.com/dashboard/site so we can better have a check?

The only place where I see I can change error reporting level to maximum is under configuration page, tab 'server'. Is that the correct spot? If so, than no error is shown on the composer page.

As to giving access to the site, apart from normal reservations I also have two-step verification. How do we work around that?

Regards,
Friso

Additional: it is getting weirder. I re-installed Easyblog, and now the composer looks as intended on one computer, and still rotten on another computer. Also re-installing using that other computer (idiotic, but that is the result also) did not solve the issue of having a chaotic composer on one computer (and not on the other)

Latest news: when I switch to another browser on the problem computer (from MS edge to Firefox), then the issue with the composer disappears. Still weird, because on the first computer the composer layout was OK also in MS edge.
We have a workaround.
I am curious if you have some kind of explanation for this behavior, for that I have left the ticket open.

I am sorry the delay of this reply,

The only place where I see I can change error reporting level to maximum is under configuration page, tab 'server'. Is that the correct spot? If so, then no error is shown on the composer page.

Yes, it is the correct setting you activated the error reporting from the Joomla global configuration page.
Perhaps you can try to view the page source then scroll to the bottom from the source code and see if there got any PHP fatal error?

If still doesn't any error on the page, perhaps you can check whether possible to disable this two-step verification temporarily so that I can able to access your site to investigate this issue quickly?

Latest news: when I switch to another browser on the problem computer (from MS edge to Firefox), then the issue with the composer disappears. Still weird, because on the first computer the composer layout was OK also in MS edge.
We have a workaround.
I am curious if you have some kind of explanation for this behavior, for that I have left the ticket open.

So far we don't have encounter this kind of issue before, by right if the issue happens on browser A, it should happen on browser B or C.