Exact same problem here.
I tried many ways: clearing jenkins "caches" dir, upgrade all plugins... the problem was still there.
Another workaround I found was to temporarily set git checkouts to use ssh with no credential at all (so using user operating system git).
In fact as soon as I set a credential to git checkout (via https or even uselessly ssh ) I had this problem. I tried also with a brand new credential. Same result.
The only definitive way to fix the problem is to downgrade to jenkins 2.291
This is a very blocking issue I think and should have a higher priority.
Same error on my side. This change changes the implementation of the iterator() method, which doesn't allow remove() anymore.
Should maybe be higher prioritized, as it doesn't allow builds at all?