EDIT:
Just did some more searching on the forum and came across this thread from 2016:
It appears to have an almost identical set of symptoms to mine and seems like it does stem from how flexbox handles sizing its children elements. However the troubling part to me is that this post is from 2016 and despite 30+ subsequent replies and multiple anecdotes confirming similar problems nothing appears to have been done about this. It seems like unfortunately while this forum shows decent response time and support for simpler issues, more longstanding and complex problems even from as early as 2016 seem to see no attention from the developers which, given how relatively simple of a test case this is, unfortunately may end up making this an unsuitable platform for my use case.