Is there any reason as to why a satellite configured as a closest server for the location that contains the primary servers would not appear in the servers list? (both ZENworks Properties->Servers and 'zac zc -l')

The devices show the correct configuration location (both ZENworks Properties->Agent and 'zac cl')
The location is set up with the satellite specified in the Location Closest Servers for both Content and Collection (with Exclude the Closest Server Default Rule NOT checked) i.e. it should list first, with the default closest servers subsequently listed, as it does on the other 30+ locations we have defined. The only thing particular about this site is that it is the main data centre site and the primary servers reside here....

ZCM 11.2.3a MU1