I have often had problems with gradual tempo changes going out of whack. I found myself just entering multiple tempo marks to simulate the gradual change (rather than figuring out what the problem was).
Yesterday I began work on a mockup of Rachmaninoff’s Piano Concerto No. 2, Movement 1, where in 4/4 time the tempo begins with units of half notes. An early ritardando between half note tempos results in the tempo number value doubling during it’s execution. This is confirmed in the top tempo readout during playback, which is also at double speed.
Because the values were doubling, I decided to see what happens if I change the tempo unit to quarter notes and double the values, and… the readout and playback worked correctly! Dorico seemed to behave as if the gradual tempo function requires a standardized unit of quarter notes to work properly, although I have no idea if this is actually the case.
If someone knows what’s going on, I welcome your instruction!