Progressive delay between live and OBS output

I have observed an issue that has been happening off and on for several months. When OBS is first started, the live input and OBS output are perceptibly in sync. As the stream session progresses, there is an increasing delay between the live and OBS output which becomes distracting for the operator. I generally do not allow the delay to be more than 1/2 second before I shut down and restart OBS, where they will be in sync again. I do not believe that you have to be streaming for this to occur, just have OBS running for a "long" time - 20 minutes and up. It does not happen all the time. The OS is Windows 10 with a 12 core i7 and plenty of RAM. Have never seen OBS to take any more than 10% of the CPU. Any ideas as to where to look would be appreciated.