I too have the same problem I have had 4.35 installed and played for months. Tried to put in U1 and U2. The installers complain: Corrupt file: “4.35.1_Part_1.bsf”.
The original 4.35 installed from the installation directory into the game directory and played fine so it seems there must be a problem doing a check on these files.
I again extracted the original 4.35 base into the installation directory again and the incremental installer still complain. I’ve never had problems with Windows Defender affecting extracted zip files.
SOLVED:
I finally realized the installers kept resetting the path to my Programs instead of my selected installation directory. All worked fine after that.
-Pv-