This Problem is a error of Immunet and not a server Problem.
The ClamAV 0.102.1 provided by Immunet is outdated and the current version is 0.102.3.
This is also reportet by C:\Program Files\Immunet\clamav\0.102.1.76\freshclam.exe and
freshclam.exe cancel the update after the download of the first "cvd" it get. ClamAV do that to prevent using a old engine with new Database files.
Freshclam.exe have problems to download and also cant update complete downloaded files.
Download clamav-0.102.3-win-x64-portable.zip from https://www.clamav.net/downloads#otherversions
Stop the Immunet Service --> net stop ImmunetProtect_7.2.8
Delete old Database files bytecode.c*, daily.c*, main.c*, lastupd and update.log
Extract the files to C:\Program Files\Immunet\clamav\0.102.1.76
Start the Immunet Service --> net start ImmunetProtect_7.2.8
Start Immunet, Click on Update Now and wait a moment (if Update does not start repead it after a min.)
The download location is configuratet in the file freshclam.conf, if you need to use a other mirror change it in this file.
Immunet need a Update to new ClamAV version 0.102.3.x
What a disgrace from Immunet