Have you tried a different phone instrument or are all these occasions were caller display hasn’t functioned correctly ( so the display shows a generic ‘incoming call’ message rather than the number calling 50% of the time , and caller display works correctly the other 50% of the time ) as it’s difficult to see how the network can malfunction with this result , one call displays OK , then the next call is not OK , it’s easier to imagine it could be the phone instrument itself ….
Normally , to prove this issue conclusively it’s necessary to try using a different phone (one with caller display ) to see if it also demonstrates the same behaviour, you could do this by borrowing one from a friend, neighbour or relative for a short period , or by purchasing one , although admittedly buying one just to ‘proves’ the issue isn’t your equipment you may regard as an imposition , but many retailers offer a no questions asked return period ….anecdotally it seems older phones with caller display can be somewhat hit and miss , how old is your phone ?
FWIW , although it’s entirely possible that it’s ‘DV’ that is the issue , it isn’t necessarily so , and ‘it worked OK on the old PSTN service ‘ doesn’t really prove anything , a different phone either working fine or displaying the same problem does give a much better indication where the problem is .
