We used a plugin by Nvidia called APEX Destruction that turns a mesh into multiple chunks set by us, and with a line trace we apply impulse and switch the normal wall with a destructible one and a second to be the "leftovers" of the original wall and deactivate the player collision response on the chunks so you can move through them with no problem. It's now discontinued, a little big buggy to work with, and can definitely not work for what you may intent to as it almost didn't for us, but it's what we somewhat knew how to work with. I would suggest studying chaos destruction from Unreal (the game is made in UE4 btw) if want to make something similar, since it's their in house implementation of what APEX did, but that I would imagine it's much more stable and reliable (even tho it's in pretty early stages).
The problems you described it's not super common but definitely not just on your end, those are part of small bugs we didn't have enough time to fix as you can see from the 15 minutes before deadline (lol), and yes! We agree on the fire thing, it was kinda rushed till the end, thats why you couldn't see it present on the first two levels.
Thanks for the review and we're super happy you got to enjoy our game! We're sure out there playing other people awesome games and leaving rating and feedback in hopes other people do the same to ours, thanks for the tip!