I think StarWarsExplained did a good summary of the question; https://youtu.be/38XI8YyekGA?t=155

It’s probably meant to imply that it’s the same rancor for more casual fans, but as for actual EU lore they’ll probably give some explanation of it at some point. This series does after all take place almost 25 years prior to ROTJ, so it’s reasonable to assume that Rancors could have too short a lifespan for Muchi and Pateesa to be the same creature. Though of course this is SW, so for all we know Rancors could live for centuries.

BTW, am I the only one who got a bit of a Kaiju film vibe from the fight between Muchi and the Brezak? There something about Muchi grabbing it by the tail and slamming it to the ground that reminded me of one of the old Godzilla or Gamera films, though I can’t remember which one.