I'm really sorry I couldn't help earlier but I see that other users suggested the same as I would suggest. avast! really has some problems with slowdowns but it depends on one PC configuration to other. I will summarise the suggestions here in case someone else is experiencing such problems:
- Try disabling all avast! Shields and check if the performance is better (You can do this by right-clicking the avast! Tray icon > avast! shield control > Disable for "N time".)
- Disable / Remove all avast! browser extensions (avast! WebRep or avast! Online Security depending on the avast! version.)
- Make sure that you don't have any other AVs installed and check if Windows Defender is disabled.
- Try running any registry cleaners like CCleaner and see if the performance is better.
Anyway, Avira is a good product as well but you may try avast! again when the new version arrives to check if the problems are fixed.
Many thanks to
@Chromatinfish 123 !