Limiting password length to "prevent hash function splitting into multiple hashes"?
The infamous "LANMAN hash" used in older Windows versions had a problem where it split passwords into 7 byte chunks and computed a hash for each separately. This, together with lack of salt, and other poor design decisions meant that a password of "keyboard42" and a password of "KeyBoarMint" store the same first value, making it uniquely vulnerable to a time-space tradeoff called "Rainbow tables" in which an adversary pre-calculates lots of data and then needs very little work to reverse an password hash.

Not only are the modern schemes you've mentioned proof against such attacks, even in the 1970s a competently designed password hash was not vulnerable to Rainbow tables. The advice you were given is very poor.