New Version : Problem with Accessing Mapped Network Drive

[REDACTED]

Having a problem with attaching files from the mapped network drive to emails.  Seems to affect Thunderbird and GMail.  Thunderbird can access the Z: (network) drive to find the file, but it just fails to show up as an attachment in the email.  Windows 10 lap-top connected to network drive by wi-fi.  I think it's an Avast update problem because :
1.  It didn't happen until the recent update
2.  When I turn off Passive Protection in Avast, it works OK
3.  Something similar happens when I go straight to GMail by using a browser

I don't like turning off Passive Protection on a long-term basis.  I've tried entering the Z: drive as an exclusion in settings. Although I'm not really sure where I should enter this, I've not found anywhere that works. 

[Eddy]

What exact OS/SP ?
What exact version of avast ? (version + build)
Any other security (related) software installed ? (or was there)

[REDACTED]

What exact OS/SP ?
What exact version of avast ? (version + build)
Any other security (related) software installed ? (or was there)

Windows 10 Pro installed, automatic updates.  Version 1607, OS build 14393.693.  64 bit
Avast Free 17.2.2288.  Build 17.2.3419.0.
Malwarebytes anti-malware installed.  McAfee Security Scan Plus seems to be there, I've never asked it to be.  Presumably another unwanted addition to a requested program.

[Eddy]

Almost all systems come with a pre-installed av when you buy them.
Remove everything from McACrap.
http://tinyurl.com/gsqzcqh

After doing so, perform a clean installation of avast.
If that doesn't solve it, disable the behavior shield and see that solves it.