RainBird Controller Only Accessible on Same SSID, Not Across SSIDs (Same Subnet)

I'm having an issue with my RainBird controller, which is only accessible when my mobile device and the controller are on the same SSID. My mobile device is connected to SSID 1, and the RainBird is connected to SSID 4, both on the same AP and subnet. I can access other devices (e.g., TESTPC) across SSIDs, but the RainBird only works when both the mobile device and the RainBird are on the same SSID. What I've checked: AP Isolation: Disabled. Firewall/ACLs: No restrictions; other devices are accessible. Multicast/Broadcast: No filtering found. Ping Test: I can ping the RainBird from SSID 1. ARP

Question by SAAD K on Super User, licensed CC BY-SA. We show a short excerpt and link to the original thread as credit.