Hi Steve, I've taken a look at the code again, and I think there is a problem with the direction change for quarter turn units, the logic only attempts to deal with things happening in the same direction. I think that I will need to try and get hold of a quarter turn encoder to determine what's going wrong here.
The problem is that quarter turn encoders are actually quite hard to find, as nearly all are now half or full turn that can be used with the existing logic.
I cannot reproduce the rendering out of order on the displays I've tried so far, but if the encoder is unstable, it could be causing jittery behaviour. If you could produce the video that would be great, also at the same time if you also turn on serial debugging that would be even better. If you are using a build system you can turn on the logging using the following build flag:
-DIO_LOGGING_DEBUG=1