This issue has occurred recently after an update but I don't know if that is the core of the problem, it hasn't happened before in this way.
Opening up any project and the preview screen and audio meter either are frozen or lagging/ the frames drop for both. (The audio plays all through fine but it seems to be an issue with the video output.
When I open a separate sequence and play footage there and go back into my main project sequence it is fixed. It does not work if I open media in the sequence with the occurred issue.
What kind of troubleshooting steps have you taken so far? Does this issue also happen with other projects? Here are some of the basic troubleshooting steps to try if you haven't already:
I noticed that you had previews rendered. What kind of video previews are they? Does the same thing happen with your video without the video previews?