wp_deregister_script was called incorrectly

L.S.,
I hope all is well. I have a question. I know this is not a presale question, but we bought the theme years ago and everything is perfect, except now with one installation. Since the theme was bought through my partner and I have not needed to use assistance before, I have no clue what my credentials for the forum are or if we even still have access. I hope you do not mind me contacting you here and with this issue.

We run recruitment sites based in the jobhaus theme. The theme works well on all our installations. All sites are set up identically with just different (language) content.

In this case I have 3 sites: the main domain with 2 (language) subdomains. All are identically installed. The sites get the same plugins, the same updates, everything the same except the editor works on both other sites (and on our other installations) and not on this one domain. It just makes no sense.

In one version (‘de’), the editor will not finish loading. I have tried, reinstalling, recloning, plugins on/off, cache empty, increase mem limit, updates, https://go-creative.com.au/tutorials/fix-avia-layout-builder-when-it-wont-load/#tab-id-2, deleted wp standard themes, etc. Nothing helps. I did notice that the slick sitemap plugin does not work well for us, so its gone now.

Debugging gives me:
Notice: wp_deregister_script was called incorrectly. Do not deregister the jquery script in the administration area. To target the front-end theme, use the wp_enqueue_scripts hook. Please see Debugging in WordPress for more information. (This message was added in version 3.6.0.) in /home/xxx/domains/xxx/public_html/de/wp-includes/functions.php on line 4773

On the forum there is one topic on this script issue, but the answer is marked private. from other topics, I could not distill a clear answer/solution or I tried what I found. Would you have any idea what I can try or do to get the editor on this one subdomain working again? Site+FTP access in private.

Much appreciated, kind regards, Rudolf