I'm going to assume it means that the client (installed app) is moving so fast (and breaking compatibility so fast) that some servers are currently unable (or don't want) to keep up. A reason to hold versions is, for example, to have more stability assurances.
The Lemmy ecosystem is going to be a mess for the next months until everything is properly oiled.
Sort of. If I understand correctly something in 18 broke captcha so they can't use it without being swarmed by bots. It will supposedly be repaired with server version 18.1. The Connect app for Lemmy doesn't seem to have an issue with the older server version if people want to give that a try. Jerboa is broken with lemmy.world currently.
Yes, that seems to be the case for most users who are currently signed in other than some random crashing. New users are unable to sign in and are currently unable to use Jerboa with server version .17.4. I'm on Jerboa too and mine is working okay for the most part. If you haven't already you'll probably see the error soon if you're running the latest Jerboa release.
Oh okay. I just checked to see if I'm due to update Jerboa, and I am. Guess I won't be doing that for a while lol. I totally thought I updated all of my apps recently.