What burns me about the lack of any attempt to explain Palpatine’s return is that Rebels actually laid the groundwork for a perfectly acceptable explanation. The blue explosion when Vader chucks the Emperor down the pit in ROTJ looks almost exactly like the smoke effect when Palpatine accesses the “world between worlds” on the show. They absolutely could have used that without getting in the weeds of the specifics of the cartoon, and just had him say that as he was falling he cast himself into the nether regions of the Force and it took some time to find his way back.

I also think Snoke should have just been an acolyte who stumbled across Palpatine and fell under his spell rather than a literal puppet. Those two changes would make it fit so much more smoothly in the continuity, but instead they opted to do it in the most inelegant and unconnected way possible.