Hi BogHog! I happen to ve the same problem : it runs a very stable 45fps, so there are no framerate drops (I'm not opening another thread since you already answered here^^)
I had the same experience with Wings of Bluestar (whereas there was no indicator of framerate, It was a very stable one, but the game seemed to run at 4/5th of its normal speed, which I could verify afterwards, when the first replays were out on YT).
The dev also thought it should be a problem with the program on which he developed the game, since my config should be able to run the game (I have a laptop Predator Helios 300, not the strongest but it should be able to hold the fort^^)
Could the issue be linked to outdated drivers, or stuff like that ?