Could it be that you were playing on a laptop and it was on battery saving mode? I've experienced that too, just today, the fps floats randomly when my laptop charger is disconnected.
I'm trying to work on a solution to make the game speed independent from the framerate, sorry about that :/
Great game, I liked the difficulty, but would like to add that it feels as if the character doesn't always jump when told to. I think this is because it is testing that either the whole character or atleast the middle of the character is on the floor, but when standing on something it seems to require less of the character to be on the floor. I got all the way through and the last one was quite a challenge, having to keep shaving off tiny amounts of time in the start to make sure there is enough time to reach the end if a mistake is made. Liked the text added as well, just expected it to be about someone else, not sure if it was an intended twist or not, but I liked it. (I tested the ledge problem I was having, it's probably not what I was suggesting and could just be input lag. I mostly found it happening if I had to do quick jumps in succession) I also quite liked the level design. Also, thanks for showing me why I used to love platforming games.
 "Overlord's New Mansion"){kind=icon}
 "Labyrneath"){kind=icon}
 "Infinity Inc"){kind=icon}
Could it be that you were playing on a laptop and it was on battery saving mode? I've experienced that too, just today, the fps floats randomly when my laptop charger is disconnected. I'm trying to work on a solution to make the game speed independent from the framerate, sorry about that :/