htop in a notebook looks kinda wonky so i would not use that.
Free gives you a general overview so with free -h or -m you can also see some info.

https://www.howtogeek.com/659529/how-to-check-memory-usage-from-the-linux-terminal/

Also trust os commands over the metrics. Nothing knows better what's going on on an os than the os itself.

But it being a shared interactive cluster: how long has it been you restarted it?  Is it always the same job that gives issues?  Are you sure nobody is running anything?
I'd check the same workload on a single user cluster and see what happens.  Shared clusters do have some limitations.