Since a bit of time (Early December ?), the developments of OpenXCom have become incompatible with the maps included in the FMP. The issue is not trivial to fix (few people are able to edit maps), so I wouldn't count on it being fixed by 26 January.
To playtest, you will have to pick an older nightly build of OpenXCom. It might be safer to double-check with Solarius, to determine exactly which version you can safely use.