I have no idea here but, as an example, I’d expect the behaviour you describe if someone tried to mix Recaptcha V2 and Recaptcha V3. They might get a score from V3 and, if that score is low, they challenge with V2 as an “escape hatch” to prove you’re not a bot. But then they might have messed it up and redirect you back to a V3 check which still gets a low score. Cycle repeats.

In fact, they may well be testing an upgrade from V2 to V3 which could behave the same if they test both at once instead of A/B test.

This is pure speculation. Probably 100 other ways they can mess it up.