Both of my 4k fire sticks were losing the VPN connection very often. I couldn’t get through a show without the VPN failing multiple times. One stick has OS 6, the other is OS 7. One of the steps I took was to install a different VPN service that I subscribe to. One is IPVanish and the other is Proton. They both would disconnect every couple of minutes. Didn’t have a problem connecting. After trying everything I could think of to fix it, I did a factory reset on one of them and just installed bare minimum addons that I use. The VPN stayed connected. When I was confident the VPN was working correctly, I started adding some of the other addons I was using. The culprit was the TDUK debloat tool in the Troypoint Toolbox. I used this tool for a really long time without any issues The VPN failed right after I disabled the functions that were disabled before the factory reset. I went back into the debloat tool and enabled everything except Alexa and shopping categories, but the VPN still wouldn’t stay connected. Once I cleared the data on the debloat tool and removed the app ,the VPN stayed connected. Both of my sticks are now working fine.
very nice process of ellimination 
Did you do a complete list enable or add and test after adding one at a time to isolate the precise one that caused your issue?
I’d sure like to know the exact process that breaks the VPN when disabled.
When I enabled everything except for Alexa and the shopping processes, the VPN still kept on disconnecting. I decided to clear all of the data and remove the Debloat tool from my device. That’s when the VPN stayed in service. I would have started enabling one process at a time if the VPN stayed connected with Alexa and shopping disabled, but it didn’t. I repeated the step on my other FireStick and had the same results.
I had the same issue only it wasn’t TDUK. To be honest forgot which app it was needless to say, problem solved… FOR NOW.