Some consumer mesh networking products collapse 2.4GHz and 5GHz into a single SSID, so it can get tricky to tell whether a given SSID is on 2.4GHz or 5GHz, as it can be both, especially with dual-band capable clients! The backhaul channel is normally hidden, but with something like inSSIDer they show up on the list.
BTW, I've had no luck getting a 868L bridge to remain connected to my Netgear Orbi RBR50 router at home (through just one stucco wall, <10 foot separation). The 868L appears to get confused about whether to talk 2.4GHz or 5GHz for this home SSID (I've seen the wireless channel jump back and forth between ch 4 and ch 36 as displayed in the 868L Status page), and the wireless link typically does not survive overnight: Connection Status becomes Disconnected, Channel becomes N/A. I've pretty much given up on this, considering that 868L is already EOL.