Hello,
I’ve reported a similar problem before, caused by fermatas. I’ve attached a short video; please note that the poco rall. (a 90% reduction) causes the following bar to be played extremely slowly, while accurate tempo then resumes the next bar after. I believe this to be a bug caused by time signature shifts not playing nicely with gradual tempo modifications.
Quick question: when highlighting the poco accel, where does the left handle of that tempo direction attach? If it does not attach to the first beat eighth note, then it would not get that tempo instruction until the “column” it is attached to plays.
The tempo equation is also further slowing your tempo for the following measure as it is telling Dorico that, compared to the tempo at the time the rit. ends, you want it to slow further where one beat in 4/4 is equal to 1.5 beats in 3/4.
That actually makes sense, but is very counterintuitive. I had thought that modifications to the tempo like rallentando modified the absolute bpm. However, the tempo then speeds up from bar two (6/4) to the bar three (12/8). That makes no sense to me, even assuming the comments you’ve made.