Performance: Godot is optimised for general-purpose cases, and sometimes games hit the specific cases it's not well-optimised for. This is true for any engine; there is always a trade off. It was useful that we could optimise GridMap for our specific open world use-cases though!
Bugs: 3.5 was *remarkably* stable considering it's a community-driven project. However, given the number of players CB has, and the number of hours each of those players put into it, we did encounter a handful of weird engine bugs relating to audio & thread-safety.