That would be a good thing for you to find out.
It’s hard for me to imagine how the user_id would be invalid.
Probably so, but you’ll want to figure out which users failed and why. Were there errors when you pasted the commands? If you can’t find that out, you’ll need to look at the users that exist and the ones that you expect to exist and see what the difference is.
If you don’t have easy means to scroll back through the stuff, you should work in smaller batches so that you can check on their progress more easily.