?? Never heard this one before! Cannot confirm it in my own gameplay as well. Are you sure the wyvern is not following another dino/player and takes off to get to it once you dismount?

I'm sure! It happens even with a fresh spawned wyvern. It's a pretty known bug on my cluster and the elimination of this issue is listed as a feature on another mod so figured I'd mention. It doesn't happen every time, but it does happen enough to be annoying. If you can't reproduce it I wouldn't worry about it, maybe it'll strike on your end sometime.

I'll see if I can find a reproducable bug... looks like something with replication of AI component. Does it also happen with the vanilla flyers as far as you can tell?

I can test it out, been a long time since I've used a vanilla flyer.

i have this issue with argies, and wyverns, they just randomly start walking away.

This is may be a core game bug, not a mod issue; although I had classical flyers installed every time I have seen the bug. To replicate the bug go in third person and look ahead of the wyvern when dismounting. This will occasionally cause the Wyvern to slowly move towards the location you were looking.