Also have been using Evernote for many-many years. Hate new updates, but continue to use EN as a lot of notes/folders are there.
Today I faced the same issue - created a note, wrote 20-30 lines of text. Then switched to other notes. Returned to the initial one, clicked the note and all lines of text except the first 2 disappeared. Undo does not work, for EN it's as if there were no other lines before. Very disturbing.