I'm glad that you enjoyed your time at ChezJJ, and sorry that we didn't communicate more with you about what happened with the downstairs neighbour. Tensions between us were definitely high during your stay, and I'm sorry that that impacted your experience.
To fill you and others in on what happened, especially since much of it unfolded after you left, I later found out that a new roommate had just moved in downstairs, and that he had accidentally gone up an extra floor when coming home. I definitely wouldn't expect this to happen again, but just to be safe we have, indeed, started locking all of our doors.
Aside from this mistake, our relationship with the downstairs neighbour has since improved drastically. After putting down multiple carpets to muffle noise, tidying up clutter in the garage, and cleaning up some of the common areas we share with the downstairs neighbour, they've become much friendlier towards us. They've since written us a note to thank us for our efforts, and I expect our relationship to continue to improve.