Its odd - could be an intermittent fault.
Have you checked first for any “known network faults”
As well as trying 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.
If nothing shows on there, try calling it in as a fault (free on 150 VM line - or 0345 454 1111 others - national rate) and see what they say when they test your connection. If they say it’s a known fault, get a fault reference number.
Or a VM person will respond on here in a day or two and take a look at the connection
I do not work for VM. My services: HD TV on VIP (+ Sky Sports & Movies & BT sport), x3 V6 boxes (1 wired, 1 WiFi, 1 on PA) Hub5 in modem mode with Apple Airport Extreme Router +2 Airport Express's. On 250Mbps, Talk Anytime Phone, x2 Mobile SIM only iPhones.