The planet has an OUTPOST. The one I was actually trying to land on. It drops me out of jump, does the glide thing then drops out of glide and just moves extremely slowly to the target, never reaching it and never letting me land. I've tried this on like 5 different planets. Same crap.
By extremely slowly, you do realize that after glide you end up with ordinary "standard" progress using thrusters (no supercruise speed) so yes, it could seem very slow.
Increase your speed and boost, to see what speed you get up to as a test. A few hundred kph can seem very slow on the surface of a planet.
If you come out of glide too far from the outpost, it will seem like an eternity trying to get to it.
Ideally, you should set the outpost up in your sights so that you descend at about 30 degrees, that way you should drop out of Glide within about 7 km of the station and able to hail it for landing permission. Fly as normal to the outpost.