On Saturday, December 24, 2016 at 11:59:38 AM UTC-8, Joseph Gwinn wrote:
On Dec 24, 2016, wrote

I have two heavy wooden doors bought 10 or 15 years ago that quickly sagged
trapezoidal in the summer heat - the Sun hits them in the afternoon. The
original doors were ratty, but never sagged. The problem is that the door
manufacturer used some kind of plastic based glue (Titebond?) that creeps...

If the joints were tight, there wouldn't be creep at any reasonable temperatures.
Methinks the manufacturer didn't use good construction OR good glue.

Did the rail/stile joints open and show a crack?