I'm seeing this with emails with the voicemail attachments from FreePBX.
Though, hum... One user reported this last week. I replaced his hard drive over the weekend and did a clean install of 1703, upgraded to 1709 and THEN installed Office 16. Issue seems resolved now.
Tomorrow, while I'm in the office, I'll poke at other Office 16 computers to make sure they also have this issue, and then see if it's an update thing or if a reinstall of Office fixes it.