There were ongoing issues recently in Belfast - see link - dunno whether they have been resolved yet.
You can always try the “check service,” Area status webpage" (link at top right of this forum), also try the “free & automated” Service Status number - 0800 561 0061 - which usually gives the most up to date info. and tells you of more local issues down to postcode level. These may not be listed on the Area Status web page (Areas are not “Geographic” they are billing areas) as that usually only covers faults affecting 1000’s of customers) so phone may give you more info, but even that wont cover problems affecting just a few customers.
I do not work for VM. My services: HD TV on VIP (+ Sky Sports & Movies & BT sport), x3 V6 boxes (1 wired 2 WiFi,) SH2 in modem mode with Airport Extreme Router +2 Airport Express's. On VIVID200, Talk Anytime Phone, x2 Mobile SIM only iPhones.