Does the VPN reduces internet speed on drone
The reason I asking this is because when I connect the vpn to my computer the speed drops down, I wonder if it is the same for the drone and that may be the reason why the video stream might be laggin or breaking sometimes.
Although we aren't VPN experts (yet), this is something I've seen myself. There are parameters that can be configured by VPN server/clients that may affect bandwidth (e.g. MTU).
There are various types of client/servers out there so it varies how these could be setup.
Also, depending on where the VPN server is located, you might be going to a server far away, and depending on the VPN server quality, they may or may be sharing resources with you.