Different program results despite same seed and hashseed

I have a program in python that relies on randomness (implementation of simulated annealing). When it is ran multiple times with same seed it outputs different results. I've managed to find out that first difference occurs in result of random.sample on a set.

Random generator is initialized before any calls to it's methods.

All tries were with same parameters, using the same software and hardware.

As I am using sets in this version of python, I am setting PYTHONHASHSEED to 0.

Used random generator is python random module.