Lost access to xs728t after deleting VLAN routing

Long story short, we have an XS728T that is configured with:

Management VLAN 99

IP address 10.99.0.1

Network 10.99.0.0/24

Gateway 10.99.0.254

Inter VLAN routing is performed by a separate pfSense box on VLAN 99 IP address 10.99.0.254.

Occaisionally we would have issues connecting to the other switches on VLAN 99, sometime they were accessible from other VLANs and sometimes they weren't. 

I was trying to track down a completely different issue when I noticed that the XS728T was configured to route VLAN 99 on IP address 10.99.0.254.  I had a bit of a eureka moment and realised that this was the cause of the other switches being inaccessible.

The obvious thing to do was to select the VLAN routing entry and delete it.  I figured that doing this shouldn't affect the management VLAN or the IP address of the XS728T so I deleted it....

And that was the last time I was able to access the web interface or the telnet interface on port 60000.  I have restarted the switch and it starts up and everything else (VLANs, LAG groups) is working.  It seems that the switch has forgotten the management VLAN.  I have scanned/searched for it on the default VLAN without success.

I have config backups so can always reset the switch and download the config to it but am wondering if anyone has any other ideas to try before I schedule the downtime and do that?  Thanks