There is still an issue with the built-in widgets library (as opposed to importing the library from Github) and Steam builds, as seen in these threads.
Essentially, the game runs fine on:
However, as soon as a build that works is uploaded via Steampipe and then downloaded in Steam, any call to the Widget library results in a crash. I know it's not anything I'm doing because OSX sees the initial build and the Steam version as the same app, so I can load the same saved game and get an issue only when playing through Steam. I thought it might be to do with the DRM so uploaded a non-DRM version and the same thing occurs.
I was using the Github version from 2016 with a few of my own fixes, but once the built-in library was updated recently I switched back to that, as it makes the project folder a lot tidier. Looks like I'll have to re-implement the GitHub version but this is something that shouldn't be happening.