Malware Protect (MTA Mode ) unscannable

http://sxg.secusolut.de/sxg/2021-05-23%2021_22_08-Window.png

Since the update to 18.0.5 MR-5-Build586, all incomming emails are blocked by the virus scanner, because they are unscannable. Everything seems to be fine since i have disable Malware Protection.