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the other way around this time... I uninstalled AIS to check if it was behind another issue (unrelated here), rebooted, saw this unrelated issue was still there so I decided to restore Windows at a time AIS was installed, ie my latest restore points... when rebooting then login in then black screen
...
Went to safe mode, got the message there that the restoring process succeeded. Rebooted into normal mode, could login properly this time. No Avast icon in system tray but I saw Avast services were running... launched Avast UI using the start menu icon: "license expired", ie all paid features were disabled. Re-entered my license, that worked. Just a few settings from the paid features were lost, no big deal... and btw all firewall rules were recreated from scratch.
Now two other small issues: when rebooting again just now the avast icon refuses to appear in sys tray, and nothing whatsoever from Avast is being recognized by Seven security center. I'll attempt a repair and post back.
ps: I don't mind the license issue, that's most likely normal, anti-piracy etc...