Whats broken with Avast on W10, I've not noticed anything yet? I haven't received the anniversary update yet though.
It is related to the secure boot driver enforcement change, it was not applied in any of the insider builds prior to the AU update so it caught many security vendors by surprise.
As I said before Win10 cannot be relied on for a stable platform where "things just work", it's code "subject to change" when microsoft deem fit. They have took on a rapid development model which some people like, but some people also dont like it. Thats why it is a love it or loathe it product.
Also it seems the AU update prevents some group policies from working on pro edition, they can still be configured but now silently fail if it isnt a enterprise or education, or server SKU.
I expect a phone call from my dad soon as well when all the data mining tasks get re enabled in task scheduler making his pc slow to a crawl again.