Assembly Reload doesn't free all managed memory... Why?

I was working on my asset (Bolt) recently and noticed I was getting ridiculously high RAM usage.

The total GC allocated showed upwards of 1-2GB (!) values.

So I thought I had a managed memory leak (not freeing a reference, etc.). I probably do somewhere. That I can fix, but it's not the problem.

I tried entering playmode or recompiling to force an assembly reload and clear the memory.

To my surprise, a whopping 1.9GB of the 2.2GB GC allocated just stayed there as a baseline memory!

As far as I can remember, reloading assemblies always cleared all managed memory (which makes sense, because nothing holds a reference to anything anymore).

What might be causing this? How can I fix it?

 

I would attach a memory profiler and check what this 2gb is. This hopefully gives you then an idea how to fix it.

 

Tried it; memory profiler hanged hard for 30 minutes on a very good computer, had to force quit Unity.

 

The 2gb is undoubtedly memory I allocated though (because I only have my scripts in a blank project and it's all managed memory); that's not the issue. The issue is that it doesn't get freed on assembly reload, which I thought was supposed to be impossible?