Have you checked on the health and status of the SQL Server?

We've had this crop up on a number of occassions and found it can usually be resolved by a restart of the K2 Service or, worse case, a reboot of the K2 server. We think we've pinned the cause down to someone attempting to delete SmartObjects when they don't have the permission to do so. It seems to result in some hanging / stuck processes of some kind, that the recycle or reboot clears down. Would be interested to hear if this solves your problem or could be a similar root cause. Since we re-iterated to all our developers that they should not be deleting SmartObjects, we've seen very little re-occurence.

I beleive you might be right about the deleting objects,  as our deployment process involved deleting a bunch of smart objects  on the UAT server which is having the issue.

However niether a reset of services, or reboot of the UAT server  managed to solve the problem.

Will have to get our SQL guy to check the health of the database on monday.