I use Musescore to write sheet music, then I convert it into MIDI for SeeMusic. I've been having weird tempo issues in SeeMusic, so I did some testing. I hope that others might also experiment with this, because my findings have been very inconsistent. Nonetheless, this is what I found:
1) If your song has a tempo, then in the next bar, there's a tempo change, SeeMusic works normally, as it should. No problems here. You can have multiple tempo changes, and no issues would arise.
2) However, if your song plays, has a full bar for a rest, then the next section afterwards has a tempo change, that second section won't show at all in SeeMusic. The song will play normally in SeeMusic's pre-rendered preview video, but the final, exported video won't show the ending section with the key change. Instead, just a long pause. I found this very confusing; the final video was missing parts from the preview.
3) However, I've found a very weird solution to my second point: a tempo "sandwich". If you end the song with the same tempo as the start, the middle tempo change won't disappear. In my arrangement, my tempo changes from 125 to 115. To prevent that second section from disappearing in SeeMusic, I marked the last note with a 125 tempo, thus, the sandwich of 125 to 115 to 125.
If anyone else can confirm these issues or experiment for themselves, I would love to hear from you.