It's going to be even worse than 50:
> Given that we've only scanned 300 out of 20,000 submissions, we estimate that we will find 100s of hallucinated papers in the coming days.
replies(1):
> Given that we've only scanned 300 out of 20,000 submissions, we estimate that we will find 100s of hallucinated papers in the coming days.
Can't quote exact numbers but when I was on the conference committee for a maybe high four figures attendance conference, we certainly had many thousands of submissions.