Pressurization issues?
 

Delta 1637 today TUS-ATL. 45 minutes into the flight the pilot orders service discontinuation and for the flight attendants to be seated. OK, seems normal. 45 minutes later I asked one of the FAs what was up. He said there were "pressurization issues." We dropped from FL 34,000 down to 25,000 and continuing the flight as normal.

Anybody ever seen this before? BTW, not complaining, better than a divert.

Whats strange about that explanation is that, if it was a pressurization issue, usually they would have to descend to below 10K feet for equalization.

< speculation >
failure of an A/C pack, and the remaining ones couldn't maintain enough output pressure at 34000

Looks like it was a B739. I fly 737s and a -900 is limited to 25,000 on a single pack, so it does look like it was some sort of pack failure/overtemp/overpressure that wouldn’t reset, so that’s the likely reason for the descent.

You are lucky that on a flight of that length it didn’t divert due to the increased fuel consumption for the lower altitude. Dispatch must’ve been able to run the numbers and confirm enough fuel onboard. Always good to have extra gas!

10K altitude would be for a total pressurization loss.
One pack out would be 25K ... I assume to lower the workload on the other pack and be closer to 10K if it were to also fail.