Zytel router suddenly unsecured - but only one one channel (5ghz)

Hi!

I noticed something strange recently, one of my router's channels is suddenly unsecured.  They were both secured with WPA2 (I think) but now only one is secured.

Has anyone else had this issue?

I wasn't able to address this through the app on my phone yesterday, so will try logging onto the router tonight via the web interface.

Thanks!