Most of the time my internet connection is, good enough, but sometimes when I suffer connection problems, attempting to place a vehicle on a jack just makes it disappear completely (the raise sound effect still plays), but the jack starts acting oddly. Putting the jack anywhere else makes it act normal, but putting it where it was when the vehicle disappeared plays the raise sound effect again, plus I'm not able to stand on the jack in that position, constantly being put back onto it like trying to go somewhere on a server with a pickaxe that's too fast. Prolly some weird state its in with the jack but I cant get the vehicle back.

This happened on our server as well. The server is on 1.16.5 along with a few other mods. Even when checking for hitboxes, the vehicle is not present.

It was weird though because, at a certain angle, you could see it as long as you are not near the plane.

Here is an image of my friend on one of the vehicles.

You could try to ask a friend to help you shift-right-click spam the vehicle, otherwise, it will be stuck there.