It looks like 1.5.5 introduced a new bug with Dolmens. At least the ones I've been doing in Cyrodiil. Others in the zone have reported the same issue.
I'm constantly falling under the ground, and getting stuck, during the Dolmen encounters. It seems more likely to happen when I'm knocked back, or use skills that leap, such as explosive charge.
Sometimes I can jump free. But, many times, not. It ultimately results in death if you can't get free.
I've also noticed many of the Daedra are now underneath the ground. See attached.