Pacing:
I feel like the game's pacing is alright, especially with how quickly Ernie moves about the map, though it does get a bit stale after some time just repairing the same thing. Plus, some of the modules went way too fast for me to keep up with, which slowed down my pace much more than it helped me speed up. It seems to be what you're going for, but make things too fast and you'll lose your players.
How to improve challenge?
I think simply adding in different modules/things for your player to do would definitely make it much, much harder. Also, there is a lack of walls within the walkable area, which makes it super easy for the player to finish one module and bolt to another. Adding in walls will make that not an option, slowing down your player naturally and force them to strategize more than now, which is just walk up, complete module, walk to the next. That gameplay's gets really stale really fast.
Do I like the current module?
Yes. It is easy to understand, fluidly implemented, and quite a challenge to fix sometimes. Well done. I just would like to see different modules for players to fix.
Abilities/Upgrades for Ernie?
Well, no actually. I am sure others answered yes, but I don't think they're necessary for two reasons. One, it would break the pace of your game. I assume the way you would implement upgrades is through a menu, but going in and out of a menu gets tedious and slows down the playthrough, sometimes quite dramatically. I feel like it would be like adding lore cards to Doom. They're nice and give players more things to interact with in the game, but they slow down the pace pretty badly. However, and this goes into how you might improve the challenge, you might add parts to a level Ernie must collect before handling a particular module. Like a wrench for the current module with leaking water. Of course, that would force the room to spawn a tool with the particular module, but I don't think that would take away from the random feel too much.
Bugs and Glitches
N/A. I didn't find any.
QoL Improvements?
Also N/A. Ernie was responsive when I pressed the button to move him, I liked the pace he moved at, and other than maybe turning the difficulty dial on some of the modules down, the game felt pretty good to play.
Liked what you guys have so far!
Eric Hillmeyer