Edit: I removed the 6x2mm magnets chess board. I had issue on a reprint, I tried a different infill pattern no luck. I had a different brand of magnets, I think the nozzle get “too close” to the magnet and the plastic spread around, making the 42 layer bad. I also believe (I waited 5 hours to put the magnets) that the plastics got cold and shrink. I will do more test but I didn't like the reprint.

layers paused at 41.

The base magnets are tricky to get all flush, some of them lineup with the magnets from the PEI base/printer and they want to lift up (I had 2 of them swapping side on me), I had to epoxy glue like 7-8 of them. The magnets for the pieces are facing the metal plate and hold strong.

Knight: Check the raw model files

I also added a “mouth” to the knight and some hair lines. It seems to print fine without support (YMMV).

Queen crown: painted, you have the choice on the new file

(If you use the .stl for the magnet you have to add them under the same object as a negative part then line them up, fix the z to match the pause (or adjust the pause line).