You can use OSM inspector and fix all the issues that are displayed in it:
https://tools.geofabrik.de/osmi

For instance a forest polygon east of Eseka is currently broken and OSM inspector indicates that there is an element of that multipolygon that is wrongly classified as outer. See here:
https://tools.geofabrik.de/osmi/?view=areas&lon=10.57602&lat=3.45910&zoom=15&baselayer=Geofabrik%20Standard&opacity=0.70&overlays=ring_not_closed%2Ctouching_rings%2Crole_should_be_inner%2Crole_should_be_outer%2Cinner_with_same_tags

A simpler way is just to look at the map and find all empty area. In Cameroon the entire country has been tagged so if you see a white patch it means a new error has been introduced recently.
