Gutenberg Get Frozen

Hi there,
since this morning it is almost impossible to use Gutenberg.
As I click on the “plus” button to add a block, the page gets frozen even for 30 seconds.

Every few minutes the page reloads and I get the message “The page has been reloaded since some problem occurred.”

I experience the problem only when I edit a post with Gutenberg, otherwise everything is fine.

The editor was good until yesterday. I have NOT added any new plugin or applied any changes since yesterday.

Does anybody know what may cause the issue?