Hi there! My player reported this crash earlier today and I can replicate it. In an environment with just Betweenlands and CleanView, getting into either the Weedwood Boat or the Tarred Weedwood boat causes a crash that completely prevents reconnecting to the world (either sp or mp). Removing CleanView alleviates the problem.

Crash Reports (basically identical):
Player's Crash report in multiplayer: https://paste.dimdev.org/eqinuginuj.mccrash
My crash report from singleplayer: crash-2019-06-18_17.12.22-client.txt

Mod versions:

• CleanView-1.12.2-v1b
• TheBetweenlands-3.4.8-universal
• forge-1.12.2-14.23.5.2838-universal

My full modlist with versions can be viewed at the bottom of this post: http://enthusiasticraft.cf/modpack-update-1-5-3/

Hmm, I thought I have fixed this quite a while ago, apparently not.
Sorry about the inconvenience, I will get this fixed soon.

This should be fixed in 1.12.2-v1c, please check if you have time and close this if it worked.