My current server is running 1.12.2 just fine. When I try updating it to 1.13-pre6, it will eventually stop ticking when converting some chunks, long enough for the watchdog to kick in, shutting down the server.

One area of the world seems to be more affected than others. It is located at about x:600, z:-200. 

Note: Mojang (Grumm) is already aware of the issue, and already have a copy of my world since June 4th, 2018 (a month ago).