At least we now know the source of the issue! Not sure where I got the idea that you were using AVG (must have brain skipped from another thread).
Other users have solved similar problems with Kaspersky by adding GSAK to the Trusted Applications (see here for example) in Kaspersky - it's disappointing that this didn't work for you.
I think you are correct that there's not much more we can do, and you are down to the two possibilities you mentioned.

Other users have solved similar problems with Kaspersky by adding GSAK to the Trusted Applications (see here for example) in Kaspersky - it's disappointing that this didn't work for you.
