OK - the mystery is more or less solved (if not deepened)!  I just checked my observatory computer and comet Lovejoy is there without problems. Its on my  'indoors' laptop that it refuses to show.  FWIW I use the 'update comets' facility routinely and I checked the actual file: it shows Lovejoy - but the comet refuses to show on this laptop. However, its not a problem now that's its OK on the observatory laptop.

Thanks to all for guidance (pun!).

Lawrence