Hi Janek, I just got the same type of message on my Samsung Galaxy S4 using AMS version 4.0.7884. Virus definition version: 150624-01. configuration version: 221

The avast message reads:

journal (in red)
/storage/emulated/0/Android/data/net.zedge.android/cache/lrucache/journal
Unknown error occurred

I also reported as false positive (report filed with my email address on file.)