In new release shadowlands, when arrived to somewhere with flight master, after i landed and start moving get insta DC. Only dh affected issue. Same after summon, u accept it, loading screen and when u start moving got insta dc… kinda annoying. 
(Every DH friend of mine experienced the same new great feature, not just me only)
Yep there’s a big thread over here:
And it’s a known issue too, the workaround atm is to dismount before taking the flightpath:
I’ve been having a similar issue but when using a kit when landing im getting disconnect. 