As the switch has two equal default routes (I guess that's what you mean), it will choose one based on some "random"/unknown criteria. In your case, it doesn't do what you want. As you're migrating from one management IP to another, one thing you can do is to set a more specific route in the switch that only points to your computer's IP. This way, another PC in the client subnet will still be able to reach the switch if you somehow mess up the route. You could also ssh to another switch in the old VLAN and ssh from that to this switch as that will be a local "intra-subnet" connection, not dependent on any routing.
Example:
configure iproute add 10.1.2.3/32 172.30.2.1 (replace 10.1.2.3/32 with your IP and /32, meaning only one IP or 255.255.255.255)
This will only affect traffic to that IP and nothing else. A more specific route always wins when evaluated against other route entries, no matter the metric etc.
If you can reach the switch on the new IP, you can then remove the IP from the old VLAN and the route associated with that, save and be done!
