DHCP issues with Route10, 24p Switches and AP's

Hello.

Recently purchased the following:
Route 10
2x 24p switches
2x AP Pros.

The customer already has their network configured on 192.168.99.0/24.

When changing the Route10’s gateway adress to 192.168.99.254/24 the switches never gets a new IP. They stay on their default subnet. Same with the AP’s

I have tried every possible thing but without luck:

Setting static IP on the switches
Resetting the switches
Resetting the router
Waiting for DHCP lease
Lowering leasetime

When plugging in the switches to another gateway they get the new IP adress in that subnet just fine.

The last thing i tried now was to leave the switches on with the router in 192.168.99.0/24 over the weekend.

Now I have lost connection to the switches and AP’s even when changing back the route10 default gateway to 192.168.1.1/24

Update:

Rebooted the switches and now they connected to the route10 gateway wich is set to the default (192.168.1.0/24)

The issue with changing the gateway subnet is still persisting though.

Would it be possible to try 192.168.99.1/24 as the Router IP field?