Numerous InDesign server crashes

We use InDesign Server CC 2014 (10.2.0.69) running on a Windows Server 2012 R2. We encounter a LOT of crashes and the crash reports refer mostly (99% of the events) to ntdll.dll as the faulting module, the other ones are MSVCR110.dll or StackHash.

What we tried: deactivate antivirus and running InDesign Server as Administrator. No luck.

Does it sound familiar to anyone?

Thanks!