PC player here:
As much as I like this game, after having played a number of frustrating hours with my friend last night (he hosted), I finally gave up. He was out activating gateways while I dug to the core. I like to do this 'manually', still, and not with a rover but that's beside the point. The point is that each and every time he took off in his rocket, I was kicked from his game. When I logged back in, I reappeared where I was kicked but most of my inventory was simply gone each and every time. I lost a number of diamond drill mods due to this and generally had to craft my oxy/batteries back from scratch which was just a nuisance. Due to some synch error I was also logged back in in our base camp, only to find out that two modules weren't there anymore but the resources I used to build them were again.
While this was certainly not 'game-breaking' in the late internet jargon that sometimes tends to exaggerate things, it was a bloody pain to repeat this all over.
Next, the 'terrain reappears while mining' bug did its share to slow me down considerably. It was much like the planet wanted to deny me going to the inner mantle. I ran around a number of caves and tried various spots do dig deeper, to no avail. The already cleared chunks of rock simply reappeared in a random fashion, making a straight effort to reach the core next to impossible. I was also nearly killed by spores of mushrooms or plants that I had clearly destroyed before.
With all this terrain bugs going on, the reappearance also caused a number of tethers to be knocked over. But the tether line still showed active to me, which of course didn't help. I nearly suffocated a number of times, because, frankly with two oxy-tanks on I don't look too ofter after its filling status.
There are a number of other things I'd like to point out that makes (my) multiplayer game a desolate experience right now:
I can't see any gateways or landing sites when flying 'hunchback' in my friend's shuttle
I sometimes can't pick up resources he mined
Sometimes when he drives off in a large rover, the vehicle is gone but the medium storages remain in mid air looking like a roof
I can't use some of the mods he crafted. I simply cannot attach them to my terrain tool or they just don't work (norrow/wide mod e.g.)
When boarding ground vehicles my friend just exited I sometimes stand beside the empty vehicle, but I can drive it while my astroneer keeps staying where he is
These are most of the issues I can come up after several extremely frustrating sessions. I don't know what and how you guys fixed for multiplayer experience but it seems to me that you still have a long road to go.