Re-starting/rebooting the VMG1312-B10A could induce the Velop Mesh to cooperate one again. That does not imply the problem is with the VMG1312-B10A, it could just as well be the Velop Mesh system.
I was going to ask if all devices connected to the VMG1312-B10A have static IP addresses or if they are assigned addresses by the -B10A's DHCP server. If the latter then I wonder if, after a period of time, the Velop Mesh system is failing to ask for a lease renewal.
One simple test would be to leave everything as it has been configured for the past two years and, when the Velop Mesh system fails, just unplug the Ethernet cable connecting it to the the VMG1312-B10A. Wait for 10 - 20 seconds and reconnect the Ethernet cable. If the Velop Mesh system begins to work once again then that would be a big hint pointing towards the Linksys system.