Ran Smart Scan which usually takes 5-10 minutes
But, it’s been stuck at 80% complete for 2 hours.
What’s up?
OI Same here. I turned to Avast free edition AV (from ESETnod32 AV previously)that I just finished installing and ran the smartscan (default settings) for the second time - as i even reinstalled avast after heeding the advice in other threads i found where they suggested an avast ‘repair’ might help fix this bug. Did you try it?? (you get the repair option when you try to uninstall avast). Might help you
I’m monitoring the scan % closely right now as I type this msg and it’s been stuck at EXACTLY 80% for around 35 min now. 
Esetnod32 had completed the scan & reported no viruses earlier b4 i uninstalled it + i also ran the basic win10 memtest and HDD scan diagnostic tests to try to rule out any hardware problems for me (everything came out fine but I have my doubts bcuz of the bsods). I switched from ESET to Avast because of the ridiculously high no. of page faults eset was giving me + the high cpu usage for eset that i noticed yesterday (eset’s good too, but i wanted to try avast as a ‘tech-savvy’ friend recommended avast and i wanted a 2nd av scan result). Avast Smartscans are supposed to be very quick <10 min (the no. of files on my hdd doesnt warrant a >5-10 min smartscan), but it isnt a comprehensive scan which I need to do next anyway and god knows how much time that’s gonna take if the smartscan itself is so slow =/
Update: Ah, it’s finally done. Total time~40 minutes o0. I suggest you try some other antivirus if repairing avast didnt make any diff. and see if that gets stuck too…if so, then check your HDD health and run memtests 2 see if your hdd/ram is the underlying issue so u can rule that out. gl 
You can customise what the smart scan actually scans for, many elements are taster (not the full paid product). Avast Settings > General > Smart Scan. Users can also uninstall components that they don’t need or want as having a component installed is likely to result n its inclusion in the Smart Scan.
There are times that I feel the Smart Scan is more promotion for other avast paid products.
There is no way that two different AV scans can be directly compared, so it isn’t a good comparison.