When I try to "modify" a host I get "array_key_exists" error

Icinga Newbie. Long time Linux Sys Admin
For eight similar nodes (and only these eight out of thousands) when I try to “Modify” the host entry in Icinga Director I get the “error array_key_exists(): The first argument should be either a string or an integer”. When I google that I see it is a common php error but I’m not sure where to start troubleshooting this in ID.
The “icingae daemon -C” check passes on the nodes and I can stop/start the Icinga services fine. I can even Inspect the node in Director, the Action link immediately above Modify on my screen. Just “modify” in ID seems to through the error and only on this small set of nodes.

I just joined the community today and I’ll start digging through the pinned topics to work on my ID troubleshooting generally but am hoping someone has seen something like my error before and knows a quick fix.