Hello,
I successfully replicated your scenario using the backup file provided. The issue you described is caused by the operation of a WAN failover services. When a WiFi WAN connection is lost or restored, the router restarts the wireless service. As a result, WiFi AP clients also lose connection with the device for a moment. If a laptop is used, the connection is automatically re-established quickly after losing just a few PING packets. However, Android devices are not able to get back to the WiFi network so quickly, so you need to wait a little longer or do it manually on the smartphone.
Basically, the long switching time depends on the end device you are using and its WiFi settings, as the WiFi service reboot on the router is very fast. WiFi reboot is necessary for proper WAN failover operation.
Regards.