LoggingLevel=5 - on both machines.
Can you change it to
7? As Vlk said somewhere, only infections will be recorder at that level. Level 7 will join much more information in the avast! log...
LoggingLevel=Emergency=0/Alert=1/Critical error=2/Error=3/Warning=4/Notice=5/Info=6/Debug=7
Ok, this does not explain the behavior of the two identical systems (just language)... I'll keep thinking.