Had an issue where I forgot to disable AV when installing U4 and Setup had a CTD without installing U4 fully.
I couldn’t reinstall U4 because Setup was showing it as already installed but in-game still showing as U3.
Rather than having to do a complete reinstall, I removed the last block of text from the file …\Falcon BMS 4.34\User\Config\Setup.ver and Update 4 disappeared from the Installed section in Setup and I was then able to successfully install Update 4, this time with AV off. Only remove the last paragraph of text, other paragraphs refer to previously installed Base and Updates.
It would be very useful if you were able to force reinstall of the latest Update from Setup even if it is already showing as Installed but this is workaround while that option is not available.