I tried this as well and got same issue when doing playback. As soon as playback reaches non-cached frame, it gets stuck and need to click play button again.
I tested by reducing the size of color solids to 10%, so in my system caching is very fast and playback never reaches non-cached frame and it works fine. Also was possible to get working by using viewer proxy mode (16 or 32). I reproduced the issue with fully new comp with few solids and one animated transform like in sample. Playback can be continued if changing the size of viewer zoom (scroll-wheel) when it gets stuck, so it seems to wait just some change to continue viewer render and caching again.
In render output to disk test I can confirm the issue as well. When render stops it’s possible to click pause and continue to get further, but render might stop multiple times during process.
I also noticed a small terminology thingy. In render controls play button (continue) tooltip is “Restart task”, which indicates to restart from first frame. But it works as the icon indicates continuing from paused frame which is expected. Can some great developer change its tooltip to “Continue Task” for future? Pause icon’s tooltip also mentions restart, so it could be adjusted as well.
System Information
OS: Windows 10 Home
CPU: AMD Ryzen 7 2700X
RAM: 32gb
GPU: Nvidia RTX 2080 8gb