Maybe you can find this interesting: I'm posting just to say that everything went well, no problems at all. I rebooted three times, and everything is normal.
Not many people come to the support forums to report that everything went, well, OK 
Fine on my XP system and about to do an install over the top (off-line installation file) on my win10 laptop. Though I may just put this off until my weekly system backup on Sunday. Though I have a backup (and Recovery Disk), I would prefer it to be a recent one rather than one that is 6 days old 
Would that most of the users reporting issues here followed your criteria: Always back up your system with a recent image before proceeding with a new install of avast or whatever program/change they are introducing or considering. If there are problems you can always go back.
Ran a laptop for a few days without AIS/used Windows Defender for protection after upgrading system to Spring Creators Update primarily to see and guard against any unforeseen issues by setting the system to Microsoft default settings first. Once that was known good, moved on to installing AIS latest version.
I also took the precaution of uninstalling MBAM anti-malware before proceeding.
I did encounter the UI error reported elsewhere in the forum. Two reboots took care of this issue as the GUI and services apparently updated twice with each reboot.
This version also reports one shield as disabled! Other than that UI error all is well and is resolved.
