Adobe Reader DC: Freezing/Not opening/Hidden Security Pop up

Hi

We have a growing number of users experiencing delays of up to 10 minutes to open a PDF or the PDF not opening at all.

This is happening with Win7 and various Win10 versions with fresh installs of the latest Reader DC. The users are spread across 3 different offices.

We regularly noticed that after opening a PDF, there will be 2 Adobe processes but no adobe Windows. One process will be about 150kb and upon closing it, a pop-up will then be shown asking if you want to open in protected mode. Once that pop up is cleared, the PDF will load.

I have tried using the Adobe Cleanup tool, rebooting and then putting on a fresh install but the issue still creeps back. The issue may not appear for a number of days but then can keep affecting the user. Rebooting or signing off the machine can sometimes resolve the issue temporarily for a day or so.

The PDF's location doesn't make a difference. It happens when opening from local machine, shared drives emails etc.

Additionally, based on other forum posts about slowness and freezing, we've set the following preferences:

Documents > Documents in recently used list = 1

General > Show online storage (both options) = Un-ticked

Security (Enhanced) > Enable Protected Mode at Startup = Un-ticked

Security (Enhanced) > Enable Enhanced Security = Un-ticked

This has now been an ongoing and growing issue since the around December 2017

Is there anything else i can try to resolve the issue.