I found a command on IJAMinecraft which has just around 32000 characters, but when I paste it in, it won't take the full command! It's not a copy/paste error, because I try typing another character in and it won't show and a character counter (WhatsmyIP.org/string-encoding-decoding or something) says its under 32767 which is the limit of command blocks.
REPRODUCTION:
Copy text that is around 32767 characters long, and paste it into a command block.
Sorry if this works as expected or its just me (NOT using modded minecraft)