I have the same problem. Android 10.6 (Can't tell exactly which version because that no longer appears in Settings > Support.)
On 5 April I made an entry in my exercise log. That was gone when I opened the note the next day.
On 11 Apr I made notes in my cognitive augmentation journal. Those changes disappeared when I switched to another note for reference and went back to my original note.
I've sent a bug report to Evernote with my activity log from this morning.