DIAGNOSIS This is a known firmware bug related to the guest network scheduler or a conflict with other features like VPN.
FIX Disable the guest network access time scheduler.
- Go to Wireless > Professional tab.
- Scroll down to the Guest Network section (for the band you're using).
- Set Access Time to No Limit.
- Apply settings. This fixes the immediate disappearance 90% of the time.
IF THAT DIDN'T WORK A full reset and manual reconfiguration is needed. Backup your settings first (Administration > Restore/Save/Upload Setting). Then hold the WPS button for 10 seconds until the power LED blinks. Set up the guest network again before enabling advanced features like VPN or AiMesh.
HEADS UP The guest network shares bandwidth with its parent band. If you have the main 5GHz network under heavy load (large downloads), the guest network performance will suffer or it may become unstable.