Do you have Windows Defender and/or any third party antivirus suites running on the SmarterMail server? I have seen similar behaviors in the past when an antivirus application begins scanning attachments as they're queried by the user. Defender and some third party AV apps do a cloud based submission which can take a little longer to complete as well which can lead to that download timing out or failing. 

If you do have AV solutions on this server a good start might be checking to confirm you have the Domains data directories excluded per our KB article here:

https://portal.smartertools.com/kb/a3249/microsoft-defender-antivirus-and-virus-scanner-exceptions.aspx

Yes I have run the powershell script excluding the extensions and the domains and smartermail directory.

Since it does work on IOS as far as I can tell if AV was grabbing something would that be different then Android?

Thanks,

Dave

Bit more info. If you DOWNLOAD the file click in the area that I have in the green square you can download the attachment and then go to file manager to view it, If you click in the red area which would just normally display the file then you get stuck on at 0%

Thanks,

Dave

Worked with ST support on this. 

Looks like Google broke something. If you set the default PDF viewer to something else and have it ask every time it works. 

Had a phone that was off for a while (months) that worked when I 1st turned it back on, but after it finished updating all the apps it stopped.

-Dave