what happens when you run the ip route command manually? same error?
I can manually create a bridge and add multiple interface routes to it and it doesn’t say invalid argument, that sounds like there is a problem with the bridge?
e.g. you should be able to run commands below:
brctl addbr test
ifconfig test up
ip route add 10.99.99.0/29 dev test
ip route add 10.99.99.0/27 dev test
ip route add 10.99.99.0/27 dev test proto static
ip route add 10.99.99.0/25 dev test proto static
ip route add 10.99.99.0/30 dev test proto static
ip route add 10.99.98.0/30 dev test proto static
ip route show
ip route add 10.99.98.0/30 dev test proto static