Has anyone experienced infections after using multi-dose vials of test cypionate? Is it possible for a previously sealed vial to become tainted with bacteria?

I recently completed a 10-week cycle of test cypionate using single-use ampoules with no issues. However, I recently started another cycle using test cypionate in a multi-dose vial and experienced infections after my first two shots. I followed the same cleaning and preparation procedures for both cycles, so I'm wondering if it's possible that the second cycle was a tainted batch and bacteria got into the previously sealed vial. Has anyone else had a similar experience with multi-dose vials? Any advice or insights would be appreciated.