Interesting observation although I have not observed something similar.
Assuming this is the case, ie chest drops are somehow affected, there are also subsequent questions one could ask:
- Is it about a character being new to the specific dungeon?
- Is it about an account being new to a dungeon?
- Is there a cutoff period, after which "luck" resets? This is because lots of veterans still have lucky strikes with their old characters, I have seen it multiple times.