Over the air Web Proxy not working

The OTA web proxy is not working from one of our PMP450i 3.65 GHz APs to a connected SM. Are there any configuration parameters that I might need to change? I’ve never had a problem with web proxy on our 5 GHz PMP450i. Not sure if this is relevant but it’s maybe worth mentioning.

We have two SMs on the AP. Both show up in the session list and on the Link Status tool. Web proxy is not working for either.
One of the two SMs is accessible by IP / web interface.
The second SM is not accessible by IP. I suspect there is a programming error and I was hoping to be able to fix this remotely using web proxy. Web proxy is handy for fixing errors in VLAN or IP address but in this case it’s looking like I’ll need to go the SM location.