I got stuck after the first wave on the first two tries, before checking other comments and learning that melee attacks might be causing the issue. I can confirm for me that avoiding melee against anyone (scooter or otherwise) solved the issue.
A good concept which is pretty well executed! The camera is stuck in an overhead view which I don't feel is intended. The game page lists that it can be changed but I had no luck with that. (I also couldn't jump with space, so I think possibly some things are always set to what's intended as build mode.)
This reminds me of Orcs Must Die which is a game I really enjoyed! If you can solve the melee softlocks and the camera issues I'd definitely like to play it again. :)