Alolan Golem "unable to match an encounter from origin game"

[justjackorwhatever]

I know what this means, btw, im just confused.

I just caught a fully legal alolan geodude and am evolving that exact geodude in to a golem, but it said the following message

i did a similar thing in XY evolving a haunter into gengar and didnt get the same message

[justjackorwhatever]

well oddly enough, it popped up with a reccomended met level and location (Route 12 which it already was!) and that just fixed it??

[Soul DS]

I don't think enough information was provided here to come at a proper conclusion, but since the met level had to be edited, I suppose it may have been that you tried to set your Geodude as a Golem without editing its level, which would be impossible in normal play (to evolve your Geodude into a Golem, you first need to evolve it into Graveler, requiring to level it up by one level since those from Route 12 are already at evolution level, thus requiring it to at least be one level higher than the met level). From what you're telling, I guess the met level was reduced by 1 or more to make it legal.