MapsForge offline maps no longer recognised
I have some offline maps which I created myself from OpenStreetMap data in 2013 and 2015. I used osmosis to generate them in Mapsforge format, and they worked fine for years.
Recently, however, they do not appear in the list of offline maps. Unfortunately I don't know in which version of Locus Pro they stopped working. I tried to re-add one by copying it from the mapsVector directory to the root of my SD card and adding as an external map: I see it now when I open the "External maps" dialog, but it's not in the list of offline maps and refreshing the list does not help.
I don't see any indication in http://docs.locusmap.eu/doku.php?id=manual:user_guide:maps_external that the software has been updated to require a particular version of the Mapsforge format (and, to be honest, I'm not sure whether the format has versions, or what version my maps would be using).