I have to say, that the support of Avast is very dissapointing. I understand that I have to pay to get premium support, but at least a contact form for obvious, bigger, non-trivial issues like mine or some kind of feedback here in the forum would be appropriate, considering Avast is making money with me anyway (ads, user data) and is somehow responsible for the software, especially serious bugs, they produce.
However, I managed to find a kind of workaround, which allowed me to rescue the data of the internal sd card at least, although stuff like contacts and SMS, which are stored in some other paths, are still lost. I connected the phone to my laptop (Ubuntu 17.10) and noticed, that there is a kind of exploit allowing me to mount the sd card even with Anti-Theft locking my phone. If I reboot my phone, there is a delay of a few seconds until Avast starts (SIM removed) where I'm able to unlock my phone and change settings or so. Unfortunately I wasn't quick enough to disable OEM-protection but I found a way to mount, in my case, the sd card instead, which I describe below.
You have to remove the SIM card, reboot the phone and connect it to a computer via USB. When booting is finished quickly unlock your phone, after a few seconds the Avast-PIN window should pop up and your PC shows your device with no folders mounted, because you have to allow data access or something like that on your phone, which you can't, because the PIN screen overlays the corresponding dialogue. But if you click on your device and another folder in turns in nautilus, the PIN screen dissapears, after a few switches, for a short time allowing to quickly accept the dialogue and mount the sd card. This worked once or twice per boot for me, so if you missed it you have to reboot and try again. I don't know, but doubt it, that this works with Windows too.
