I'm sorry, I should have been more clear....shutdown the hub, pull the power cord, then plug it back in. Reboot does not always reset the radio modules in the hub. They remain powered on during a reboot.
From what I know, there is only one join process running at a time. Hubitat did change a bit when it comes to the countdown timer. Yes, it actively looks for new devices for 45 seconds but it will continue to try to join a device that hasn’t finished the pairing process beyond that 45 seconds. That’s why devices might finish after the countdown timer is done.
In regard to the second window, I am not sure if that restarts the join process or just piggybacks on the existing one
Oh, and something to keep in mind. Anyone that has joined bulbs to their Hubitat (outside of Sengled bulbs) can expect some kind of problems with other Zigbee devices. Either during the joining process or even afterwards with devices not communication anymore.
Smart bulbs are horrible repeaters and WILL create havoc for other devices like sensors or so