[SideburnsOfDoom]

> First, I explain that garbage collected applications don't release memory immediately. ... I point out that the behavior they see is normal

yes, this is an easily overlooked point: Using memory when it going free is by design. It is often better to use use up cheap, unused memory instead of expensive CPU doing a GC. When memory is plentiful as it often is, then it is faster to just not run a GC yet.

You're not in trouble unless you run short of memory, and a necessary GC does not free up enough. Then only can you call it an issue.