Was loading commandblocks in redstone chunks, loaded a particularly large command, but below the maximum limit. Each time I edited the command(s), there were several very large ones) it would kick me, AND OTHER PLAYERS within the redstone chunks off the server. I continued adding large commandblocks. At a certain point, maybe 10 large ones, I stopped being able to log in entirely as I would just keep getting kicked every "tick" with the following error: "Malformed JSON at line 1 column 1". There is no powered redstone. None of these are repeating. I just get kicked when the chunk loads after login.

At the time, I was using a bunch of "1 block installers". On retrospection, perhaps commandblock minecarts loaded with large commands (but several characters below the limit!) may be to blame? I'll have to try to recreate the scenario on a fresh backup of the map.

Researching further, I upgraded the "corrupted" map to the 34d snapshot, and the corruption still kicked me. We ran an kill @e[type=MinecartCommandBlock] , and were able to log back in no problems. So it must have something to do with the minecarts.

Additionally, running the one-block installers in singleplayer creative mode in 34D I was unable to recreate the problem.

When upgrading the online server to 34d, and attempting to edit the large commandblocks again, I now get the FOLLOWING NEW ERROR

Internal exception: io.netty.handler.codec.DecoderException: java.lang.IndexOutOfBoundsException: readerIndex(1) + length(1) exceeds writerIndex(1): UnpooledHeapByteBuf(ridx: 1, widx: 1, cap: 1)