Issues connecting to one of my clients.

I have around 100 clients across the US that I administer. In the past 3-4 months, I have been unable to connect to one of my clients PC's (2).

On one PC (Win 10) I can connect to the dashboard, but never the PC (connection fails).

On the other PC (also Win 10) I cannot even get to the control panel.

Both show version 13508 in Central.

I assumed issues with old infrastructure, and have replaced everything except the cabling in the walls (DSL modem, Luxul router and Luxul switch. We even upgraded the DSL speed from 10 mbps to 25 mbps.

I am at a loss, I cannot find any reason that would cause me to not connect after many many years of no issues and no changes other then PC upgrades.