Interesting and strange. Would it be possible to capture what you see somehow, so I might get an idea what’s happening?
Which device is that? It might make sense to first install the latest OS, to ensure this isn’t some issue with an older OS version.
The memory usage is expected to look like this: Video playback results in a bit of memory fragmentation and it takes a moment before it stabilizes to what’s actually needed. 200MB usage is pretty low, so that’s all good.