Hi,

While we are trying to recreate the issue on our end, as we haven’t been able to yet, please try clearing any cache plugin cache, one possibility could be while backend block code serving latest version, cached editor JavaScript mismatching with the backend.

I apologize for the inconvenience. 

We have tried to recreate the issue with different setups, we haven’t been successful on that yet. But we will keep trying and I will reach back as soon as we have something.

Kind regards.

I found the problem on my install, it was with the Gutenberg Block Editor Toolkit – EditorsKit https://en-gb.wordpress.org/plugins/block-options/

Simply disabling this plugin fixed the issues with being able to use UB in Gutenberg. I think I used the EditorsKit once to do some formatting quickly, so I can live without that plugin.

We haven’t been able to recreate this issue on our end.

Would any of you be willing to share a temporary access with us so that we can check this issue out?

Please let me know.

Kind regards.