That happened when I changed the map from version 10.55 to 10.78 and converted again in 10.55, didn't pressed "Yes" to reload the missing monsters and overwrite anyway.
To retrieve my monsters back , I pasted the remaining spawn monsters from "map-spawn.xml" to an old file "map-spawn.xml" (with the old spawn monsters) , so I got a single file with the old and new spawn to replace instead the other.
Obs.: Some creatures get duplicated, but the RME discard one of those, so, a single save (ctrl+s) fix your file getting 2 different files of type "map-spawn.xml" bounded!
