Ok, it wasn’t the update to 1.8.10 that corrupted your notes and reverting to 1.8.9 won’t fix them.
I am not sure how you have Obsidian setup to run on a USB drive, but your best bet is to look at the file recovery plugin (which is NOT a backup solution). See if there are older uncorrupted version of your notes within file recovery.
This type of corruption may happen if your computer crashes or, since you are using a usb drive, if you unplug/usb disconnects while Obsidian is writing on that specific note.