The charm changed name. The original charm name was 'nrpe-external-master' ('name: nrpe-external-master' in its metadata.yaml). The upgrade-charm --switch was attempting to change it to a charm named 'nrpe'.
The upgrade using the 'nrpe' charm on the local filesystem failed. The upgrade using cs:nrpe from the charm store worked.
The charm changed name. The original charm name was 'nrpe-external- master' ('name: nrpe-external- master' in its metadata.yaml). The upgrade-charm --switch was attempting to change it to a charm named 'nrpe'.
The upgrade using the 'nrpe' charm on the local filesystem failed. The upgrade using cs:nrpe from the charm store worked.