So in my alternative post, Nou had commented about a message I'd seen in the log file (and dismissed!) about a
phonon error or warning
. I'd seen it in the SGL post and as mentioned, ignored it for now.
Seeing Nou's comment, I'd disabled the SOUNDS only but instead wrote warnings to a text file so I'd be able to see warnings or track them back.
Just started another simulation with ALL notifications OFF, and also disabled the "low resources" mode - it looks like my memory usage is more stable, although that's only after a short period. I'll leave it running and come back with another report later.
There was also another update released recently for lots of Indi updates, so if the issue is fixed, it could have been either - I'll test again later with notifications back on and see what happens.