I recently reinstalled macOS on my MacBook Pro which is now on macOS 10.13.5, which isn't the latest version because I used an old macOS High Sierra installer. However, when I opened the Mac App Store to update to 10.13.6, it didn't show any updates. I thought it was an issue at Apple's side, so I downloaded the macOS 10.13.6 Combo Updater, but that didn't work either. It gave an error: "This volume doesn't meet the requirements for this update". Is my installation corrupted? If not, how can I fix it without another reinstall?
This is a MacBook Pro (Retina, 13-inch, Early 2015). I have enabled FileVault after installing macOS and it is still encrypting (about 13 hours left).