Another weird #HelixEditor thing is if you have multiple splits, and you open a different file in that split, the original file is still open in a buffer in the background. If you then use the file picker to open a file that’s already open in a background buffer, the changes you make aren’t reflected in the buffer and vice versa. Again: data loss.
Seemingly the most difficult thing to deal with in #HelixEditor is when you have multiple splits open, and you accidentally hit Ctl-W to move between them while you're still in INS mode. The behavior seems undefined, but usually results in data loss.