Did you find anything of use in the aswboot.txt file, it can be very large and much of it.
Scan History is normally in the associated text files (they are named the same as the scan name) in the C:\ProgramData\AVAST Software\Avast\report folder, see attached image.
The chest folder (externally) isn’t of much use as:
The files in it are encrypted.
The file names are also changed.
This is to prevent them being extracted and or run.
Viewing the virus chest from within the avastUI, is preferable.
What did you try when trying to access it from the avastUI ?
Did you try accessing it directly from the avast tray icon, see attached image.
Have you tried a repair of avast:
Vista, win7 or later - Control Panel, Programs & Features, uninstall a program, select ‘avast! Anti-Virus,’ click the Uninstall/Change and select Repair, click next and follow.
I found history etc on the"select folder to scan" screen. I hadn’t opened that screen since the boot scan so history etc may have been there all along.