I have the same problem on a Samsung Galaxy Tab S5. It was working fine until the start of September 2021. It's unusable in the feature rich Zoom client - I have to join via web. I've just installed 5.8.0 and that hasn't fixed it 😞
I have had the same problem on my Windows 10 Linx tablet, since upgrading Zoom last week. The camera is rotated at the start of every meeting. I manually rotate it, but then if I turn my camera off and back on during the meeting, it has rotated again.