So sometime last night, my antivirus software decided to add infra.exe to its virus chest, preventing the game from being able to launch. This caused it to go into an endless cycle of "Validating" on Steam whenever attempting to launch.

After much hair-pulling, I was able to launch the game successfully by opening Avast and restoring infra.exe file, then going to Steam > Settings > Downloads > Steam Library Folders, right clicking on my game directory and selecting Repair Library Folder, then restarting my machine, and letting it complete yet another Validation check. I didn't want to delete the local game cache due to the large size of this game.

I've sent the infra.exe file to Avast for analysis, so hopefully it will not be detected in the future. False positives like this do sometimes happen with Avast, so if anyone else experiences this issue, hopefully my instructions will help you out.