Something they could have done inside Python is manually implement a short-lived objects space that lives entirely in pre-allocated memory, preventing the repeated allocations.

I should have mentioned that the app in particular was running python2.7 - some preliminary tests on porting to python3 seemed to indicate that the issue was significantly less severe there, though the problem only occurred very infrequently that restarting the affected processes when they started exceeding a memory threshold was a more cost-effective solution that spending ages debugging the interactions.