How many subnets can a rack controller support simultaneously?

I’m running into inconsistently successful commissions/deploys against rack controllers that host a large number of subnets (they have a lot of interfaces). The rack controller itself is practically IDLE, however PXEboots fail occasionally with netconn_connect error -10 and during boot, Hitting enter will usually continue the PXEboot failure and succeed. However during boot ocasionally connecting to the MAAS metadata endpoint seems to hang and eventually fail out a lot more than expected. During these the rack controller is only service requests for a single subnet. The machines being provisioned are using HA DHCP helper to the HA rack controller(s) for that subnet.
netconn_error

Any ideas?
maas 2.9.2 (snap, stable), the regions are 3 region controllers in a HA config as per maas documentaiton.

during boot on a failed boot it tends to sit at one of several places:

It’ll eventuall end up at an “ubuntu login” prompt, and since it doesn’t show it’s hostname as declared in maas, this teels me the metadata fetch failed…

The only solution is to reset the instance and hope it works…