Can't access ex6250 web interface

I set up the EX6250 to work on my network, including updating the firmware, but changed the IP address to a static address - 10.0.0.35 with subnet mask 255.255.0.0 and 10.0.0.1 as the gateway. I checked I could access the web interface after making the change, then switched it off and moved it to a new location.

Once it had powered up in the new location, I tried logging into the web interface again, but just get timeouts. I can ping the IP address 10.0.0.35 with no trouble, and it's turned up on the ARP table of my firewall. All the lights are green.

I cleared the cache and cookies from the browser and also tried another browser. No luck. Any thoughts?

And yeah, I tried turning it off and on again.

EDIT: I tried connecting from a machine with an IP of 10.0.0.99. That worked. I double-checked, and I'd definitely set the subnet mask to 255.255.0.0, but it's acting as if it has a mask of /24.