Yeah so, I refuse to continue to pay Microsoft monthly for something that doesn't perform well. Let's face it: they are not going to bother to fix this unless the amount of people pissed off and cancelling their subscriptions is greater than the amount of people who pay them each month for subpar service.
I have canceled my Realms subscription and signed up for Shockbyte hosting - same cost, more RAM, easy to import saved worlds, so many extra things I can do with their support that I could not do with Realms AND my friend can now log in and play with us without being kicked every 5 seconds to 5 minutes. We've had 3 whole days of fun together without a single frustrating moment. Added bonus: less lag, faster loading, better user management, and stellar customer support. All things Realms sorely lacked.
Update: still not resolved!
A friend of mine has been able to join my Realms server since the 1.17.2 drop. We have already tried all of the trouble shooting tips mentioned here and elsewhere, short of "try another internet connection" because she does not have access to one. (Her computer doesn't have wifi capability, so her only option is direct wire.) She was able to access my Realm prior to the 1.17.2 drop.
We had hoped with the drop of 1.18 the issue would be resolved for her, but she still cannot join. Ten other people, located in various parts of the world, have no issues joining Realms. Only her. She can join ANY OTHER Minecraft server without issue. Which really seems to point to it being an issue with Realms coding and the internet connection, not only the internet connection alone.
Tell me, why should I pay Mojang/Microsoft money for THEIR private server service when I could throw my money at another service and actually get to play with ALL my friends? This is an option I'm seriously considering at this point.
Note: When the 1.18 drop happened, we started a new world in Realms. She was able to join at first, move around, pick up things and put them down, no problem. But as soon as she went through a Nether Portal she was immediately kicked, and after that every time she logged on she'd be kicked almost immediately.
I tried running a command to teleport her to different coordinates, in case she was stuck in limbo between Nether and the over world and some sort of internet bug was causing the error when loading between worlds. It stopped the immediate kicks for a little while and she was able to move about in the over world again, but after a few minutes they started happening again (still in the over world) and the tp trick didn't work any more.
None of this has resolved this issue for a player on my Realm. Up until the latest update, she was able to join and play just fine. After the 1.17.1 drop, she's constantly kicked from my Realm. It can be just seconds after joining, or 5 minutes after joining, but she cannot stay connected and gets the "Internal Exception: java.net.SocketException: Connection Reset".
We have tried everything listed above, and other solutions we've found elsewhere. Nothing seems to resolve. We thought we had it fixed when I purged her user data from the Realm, but after about 10 minutes or so she was booted again. Short of creating a whole new Minecraft account (which I must note isn't free to do) we've run out of ideas.
This seems to happen to ALL Realms she tries to join. Other multiplayer Minecraft servers she has no issue with. Which makes me think it's a Realms-specific problem, not an internet connection problem. Don't make us wait for 1.18 to drop to fix this issue!!
This is obviously NOT resolved - please stop lumping this in as being the same Firewall issue, because it is not!
Edit: There are other players on this Realm that can connect and play without any issues. Only this ONE player seems to be affected.
Still getting alternating 500, 502, and 504 errors. One time it gave me a 504 error, I hit "ok", then it thought for a bit and loaded the game. I played for a bit, wasn't kicked, logged out of Realms to see if I could log back in and not lose any progress, and then got the 500 & 504 error again.
Not sure if this matters or not, but the 'screen shot' for my Realm shows an image of a mini-game, even though up until the 1.16 update we've been playing in a world and not a mini-game. (It also takes FOREVER to load the Realm World thumbs under Configure World.)
I find it laughable they still have this marked as resolved when it clearly is not.
As I no longer have a Realm subscription, I am unable to test your theory, but you may be on to something. We had tried completely deleting my friend's user information from my server (by downloading the file and then editing user files and then uploading the new files) but that gave us all of 10 minutes of playtime before she was back to being constantly kicked.
I wouldn't know how to go about disabling the whitelist of a Realms world, though. I assume it's another matter of having to download the entire world, manually edit files, and then upload?
The massive delays are an obnoxious side effect, but if users are no longer being kicked then it definitely uploads my belief that this is definitely a Realms server-side issue and nothing to do with anything on the user end.