Every year I have to check my newly planted onion plants every day until rooted as they have a tendency to try to escape. Most are laying on the ground next to where they were planted, but sometimes I find them a foot or two away! Someone once suggested that this was caused by nightcrawlers - I do have a lot of worms but none large enough that I would classify as nightcrawlers.

Does anyone else have this issue, or know why the plants pop out? Had to replant a dozen so far (out of 270), which is typical.

Probably a critter.

I had the same problem with newly planted garlic cloves. Whatever bird or animal dug them out, they decided not to eat it and just flung it aside. After a couple of years having this problem, I decided to mulch and chicken wire the top immediately after planting.
Too bad that wouldn't work for onion plants!