Day One FixesAchievements Not Working Correctly
Suggested fix (unconfirmed): Wait for the developers to upload the fix to Steam within a few days.
BoneTown: The Second Coming Edition Fixes: Crashes, Errors and How-to Answers
3 fixes · 3 how-to answers · Steam discussions
Fixes and known issues
The Game Does Not Start After the Last Update
delet everything inside your workshop folder
CTD on Launch Fix
My guess is that Steam might be screwing with your resolution. Try the following, since what I gave before was essentially the nuclear option that I used myself and only resets the game, but not Steam (especially if you've changed the resolution via Steam before): 1.
How-to
The Mad Capper Achievement
No confirmed fix yet. Players suggest: Haven't tried it yet.
How to Start Game
Suggested fix (unconfirmed): Wait a minute or two after hitting play, and do not open any other apps or switch to your browser while the game is booting up. If it still fails, kill the "Bowntone.exe" process and try again.
Steam Achievement Issues When Downloading the DLC
Suggested fix (unconfirmed): Update the game through Steam to the latest version. Play the game to trigger and unlock your achievements now that the fix has been pushed.