RGP: The Minhag Lubavitch is for men not to wash on seudah shlishis. To rehash stuff that has already been said on the CR: the Rema holds you can be yotzei shalosh seudos without bread. The Chabad minhag of avoiding bread seems to have started with the Tzemach Tzedek (according to posters here).
Milhouse:
“The origin of not eating fish with milk is definitely NOT a typo.”
“Almost all Ashkenazim rely on the Ramo, who says that the Beis Yosef made a mistake, נתחלף לו בשר בחלב”
By “typo” people might be referring to the shittah that it’s a mistake/he didn’t really mean it. Clearly that shittah is not “definitely” wrong when all Ashkenazim hold of it.
I might just be misunderstanding your point, but where did you get the idea that achronim never hold that something in the S”A is a copier’s mistake?