Glad you got things working again. Keep in mind that the Gutenberg plugin isn’t actually recommended for production/public sites, so you might want to turn it off completely:
Are you a tech-savvy early adopter who likes testing bleeding-edge and experimental features, and isn’t afraid to tinker with features that are still in active development? If so, this beta plugin gives you access to the latest Gutenberg features for block and full site editing, as well as a peek into what’s to come.
If you’d still like to figure out whether it’s a plugin or theme conflicting with Gutenberg, using the Health Check plugin‘s troubleshooting mode will let you do that – without changing your live site at all. If the problem goes away after deactivating plugins temporarily in troubleshooting mode, you could then reactivate them plugins one by one (while still in troubleshooting mode) to find the culprit. If you switch to a default theme and the issue goes away, you can then reach out to your theme developer to let them know about the issue.
Since features of the Gutenberg plugin are eventually rolled into core, it could be an idea to keep troubleshooting, but it’s up to you of course. ??
I’ll mark this issue as resolved.