Bugfix release 2.7.2 was published, eliminating problem with DB cache.
The RDBMS cache implementation turned out to suffer from a race condition. It is not happening often but consequences might be severe, as Unity may answer with stale information. For installations of 2.6.x and 2.7.x versions which can not be updated immediately, we advise to turn off the DB cache (assuming you use relational database store):
As the fixing the cache would be by far not trivial and would make the caching layer even more complex, we decided to fully remove the DB-level cache. Instead a series of smaller optimizations were applied as well as a simple cache of authorization layer was added. Together performance should be pretty comparable as with DB cache layer while stability is greatly improved.
Download the fixed 2.7.1 from Downloads