Python memory leak which is not recognized by profiler

Question

The program can work fine for days, but at some random point it starts growing ~60MB/hour.

1. Profilers like guppy and pympler doesn't show leaked memory. (they show ~30mb used, while ps resident memory use is 1,5GB)
2. Gdb-heap C profiler shows a lot of chunks of memory as 'uncategorized'.
3. Gc.collect didn't show garbage collection problems.
4. We don't use any non-default C libraries, so I don't think it's C level leak.

Is that a dead end? Can something else be done to find the issue?