The problem I experienced was with pages either created with, or converted to, blocks. I was able to edit them with the Classic editor and see the block code in the Text tab. But when trying to edit with the block editor using the switch to while in the Classic editor, or edit with from the Pages entry, There was an attempt but only the link displayed and the page was blank.
However, based on your disable suggestion, I created a test site with just the Classic plugin. My test did not replicate the problem. The site where I encountered the problem has been converted back to all Classic and I don’t have the time to attempt to try to figure out if another plugin, or something else was involved. The problem was not evident on 6.6.1.
