For some reason I haven’t been able to open the map back up since restarting my PC and opening the project through the epic launcher on the same engine version.
The build settings were “Windows 64-bit” and “Development” with close to default project settings. Since I’ve been unable to recover the map and ended up deleting it and make a new one I haven’t had the issue again, but I have yet to start messing with trees and foliage on the new one yet, so I’m unsure if that was related to the issue.