When I start a timer on my vivoactive 4, the display get's all messed up then after a few seconds it all works well.
This video demonstrates the issue:
https://photos.app.goo.gl/94YjgPdtppZSvNrNA
This wasn't happening on prior software updates, also, this only happens on the timer, which makes me believe that the watch is just fine and this is a software bug.