Kaz

Correct, it happens in both survival mode and creative mode using Elytra. The spectator mode issue was in addition to that, it just has the same behavior.

Still happening for me in 15w45a with Elytra and spectator mode.

I'll try to recreate the issue on a server, but so far I can't recreate the issue in single player. I did discover that it only affects me when in survival mode, and never in creative.

I can confirm that this bug is still present for me in SMP in 15w42a when using an end portal. The exact same overworld coordinates carry over, resulting in the player falling into the void.

Yeah, I would agree with that conclusion. In my case it was the water flow updates and large scale piston shifting. Hopefully they will fix it sooner rather than later.

I just did some testing with a friend. If I turned all the farms off, she could stay on. If I turned the witch farm on, which involves tripwire, redstone and piston powered block shifting (about 128 slabs shift back and forth repeatedly), she got booted. If I turned on or off the slime farm, which involves a lot of flowing water updates, she got booted. It seems that whenever the server is getting taxed with block updates it booted her. We tax the server much, much more with high mob and entity counts at other locations(getting the server can't keep up messages and all). But this seems to be more about block updates.

Edit: All these things never triggered this issue for me in 1.8.

I removed all signs after reading a comment you posted earlier. It didn't seem to change anything for me.

It's an area in the middle of the ocean with an iron farm, witch farm, and slime farm, each dispensing their drops into water streams funneling up into one item elevator that goes into an item sorter. It's an isolated area and those are literally the only builds around. So at any given time there's maybe 20-30 items traveling through the system. I have much more redstone circuitry and higher yield farms elsewhere on the server, but they've never been an issue. I can definitely afford to abandon the area, it's just an inconvenience haha.

Thanks for the suggestion. I went and tried deleting the whole area with the command blocks in MCEdit. Unfortunately the problem persists for me.

I currently have four command blocks on my server, all simple TP commands. They were placed in 1.8, before the recent command block update. I tried both replacing them and removing them, but I still seem to have the same issue.

The server always keeps on running just fine, but sometimes it crashes the client of the person disconnected. It's odd.

I've been having the exact same issue on my server with the same output message in versions 15w35e-15w36d. It can only handle one player in an area and boots the other. This happens most often in the spawn chunks, but has happened elsewhere in the Overworld as well. So far the nether seems unaffected. I think it only happens when the spawn chunks are loaded, so perhaps they have some sort of issue? It's really got me worried that I might have to abandon my spawn area.