When I change chunk (move from one chunk to another), there's always a freeze (edit: as said by Jay Eff in the comments, it starts a while after first loading the world for me too). See 2018-10-26_11-03-24.mp4 for illustration.

Happens since 18w43a.

Also, it doesn't happen on Minecraft 1.12.2 or 1.13.2.

Tested in 18w43c :

2018-10-26_11-03-24.mp4

latest.log

^{Launcher profile :}

"1af83bf96f3edd2089a6f2e172a92549": {
  "type": "latest-snapshot",
  "lastUsed": "2018-10-26T09:21:54.647Z",
  "javaArgs": "-Xmx4G -XX:+UnlockExperimentalVMOptions -XX:+UseG1GC -XX:G1NewSizePercent=20 -XX:G1ReservePercent=20 -XX:MaxGCPauseMillis=50 -XX:G1HeapRegionSize=16M"
}

^{(Personnaly confirmed this bug in 18w43a and 18w43b (and not present in 1.12.2) with default unmodified profile = without custom java args)}