Placing an old alpha prefab into a new alpha

[Nomado-Coyote]

So I'm trying to transfer my old base from A20.7 to A21.1 now. using a saved prefab from the old version. and it shows up on prefab editor and even on world editor when you import a saved dynamic prefab and get it inside of the world. it has lots of "missing piece"s with the blue boxes with question marks, but I thought it's not a problem. I mean whatever, they're missing, so I'll just place new stuff in those places afterwards.

but when I place my old prefab with all those question marks inside a world editor, save the world and re-enter world editor - my prefab is not there anymore. the blue area box with the name of my prefab is in place, but the actual house isn't.

I wonder what's the problem, I have only 2 ideas, and I would love if somebody can clarify and guide me in the right direction how to fix this.
so firsly, I think it might be all of the missing pieces placeholders? do I need to delete them manually so this prefab is clean and compatible with the new alpha and then it will save in place? is that the problem?

or secondly, could it be because of me placing it in place of an ingame POI? the base is a captured and rebuilt ingame house. a remade POI. so when I go into world editor I just find that old house in Navezgane and just Z-select and J-delete it all, and place my own base on top of it, so as to recreate how it was before in my old game. could this be the problem? do I need to clear the area out more so it doesn't get overridden by the default POI even after saving stuff? I mean I still have the default area-box for the default POI of the building in my world editor. do I need to delete the area of the default building somehow for it not to pop-up again and again even after I delete it with J and save and reload?

[Desert Rat]

Did you update your prefab for A21? There is an updater tool for updating prefabs to the newest game version. Start the game, press F1. Type "prefabupdater loadtable", then type "prefabupdater updateblocks". It will take a few seconds. Then, go into the POI editor and load your POI. Delete / replace all of the blue blocks, then be sure to Save the POI. Once you do that you should be able to place it with the World editor. Once you place it, be sure to Save the world. Note that you will probably have to start a new game with the map. I've tried placing custom POI's into existing maps, and it never works for me.