You should definitely wait for the "malware analyst" to get in touch with you that
Alikhan has arranged. Doing so will eliminate any possible issues that may exist that is causing the missing Avast context menu scanner.
That said FYI, (to do this is for EXPERIENCED users ONLY) there is a way to
Add Any Application Shortcut to Windows Explorer’s Context MenuAgain, this is really intended for information purposes ONLY and clearly must be done by an experienced person. But I thought I'd just put this out there so that you know that this can be done and if by chance this issue is not ultimately resolved then perhaps you would know someone familiar with making changes to the computer registry. It is a simple tweak, but you should know that making changes to the registry can also cause a lot of damage if it's not done correctly to the point the computer will not even work properly if a mistake is made. (of course the registry should always be backed up prior to making changes as well, which an experience person would know about as well, just in case a problem arises as a result of the change to the registry).