Sometimes a simple layer (visible layer, no group, no locked, no alpha locked, no inherit alpha) is blocked and I can not work more, If I try it this warning appears: "group not editable". The only solution I have is delete the layer.

That's definitely strange. You might need to submit a bug report, and attach a sample file.
Is this layer inside a group layer?

No, the layer is not inside a group, this happens suddenly in any layer, without any apparent reason. I have not found any reference about this problem. I have been using krita for a short time and I have always been this problem, I think I'll uninstall the program and reinstall it and if it recurs I will submit a bug report. Thank you.

I'm having this issue too all of a sudden with the update to 2.9.4.7. I don't remember ever having this problem with 2.8--did anybody submit a bug report yet?