Thank you for your feedback! A feature (that I'd forgotten to document until now) is that running into the patches of small asteroids/"space junk" causes the player to temporarily slow down. Could this be what you're describing?
In any case, our level designer (as well as the rest of us) have learned a valuable lesson in difficulty curves, and ramping up object size is one of those changes we're working on for an updated mobile release. I hope you'll stay tuned!
-HLM, artist/concept