Why bulk plan runs much faster for an user than for another? Any ideas?

Summary:

I have 2 users with same access grants, same user domain, using same user role and planning same data set. Bulk plan runtime is drastically different between both users. One user takes hours more than the other. That is consistent across many runs.

Logging is off for both users. Matter if fact, no logging is on for any user.

Any idea what could be causing this runtime discrepancy?