Firstly did you connect the orbi in the correct sequence - see below - if not set it up again.
I would try a new Cat6a ethernet cable as old ones can and do fail, dropping speeds down to <100Mbps
What speed do you get on a device connected on a known good Cat6a ethernet cable connected to the other port on the first Orbi?
Switch on and set up your own router/Mesh unit (in its settings) with the WAN port set to be in Automatic IP i.e. DHCP (& Nat) mode, it may be pre-set that way anyway. Then, disconnect all cables from your new router (or Mesh first unit) and switch it off and unplug it. Then, put the VM Hub into modem mode ( https://www.virginmedia.com/help/virgin-media-hub-modem-mode ) and wait for the base light to turn magenta/purple (on a Hub3 - but not on a Hub4!). Once it’s in modem mode, the VM hub “MUST” then be powered off. Switch your router on and make sure it’s fully initialised (leave 5 min) and then put in the ethernet cable from its WAN port to the VM hub (any port will do).
NOW… power up the VM hub and wait 5-10 minutes for The Hub to initialise and and you should get a connection. Use the recommended App to connect any other Mesh units to the first one. This order only needs to be done the first time you connect the router to the VM hub.
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.