playback to slow

Hi, since some weeks I feel that playback of my reaper projects sometimes is a bit doughy. It's like 5 bpm slower than normal. Sometimes after a while playback rate is back to normal. Even though I have a ton of plugins loaded etc. CPU usage seems normal (10-25%), RAM 3GB (of 8) is fine as well. Some of the most complex projects even run at normal speed while others dont. I just cannot figure out what to do when its slower than normal or what the issue is. :( Any ideas? PS: Reaper v5.11, Win7, 64Bit, i7 Core, SSD

silly question, did you double check you had the playback rate set to 1.00?

If at 1.00 is it at all possible that you might have recorded wav file parts at the wrong speed then returned the project to 1.00?