A guess about a couple of things with Galaxy S8 and S9
Sometimes Bluetooth "on" interfers with wifif connection on these devices. Not the most common authetication error, but try to eliminate this as a problem. Try it for a few hours with Bluetooth off.
Try rebooting the router of course, but since this is happening frequently this may not be the solution. Rebooting the router may only be a temporary fix reassigning IP addresses.
Forgetting and reestablishing your network connections assigns new IP's and you get connection.so this may be why you can connect after going through the gyrations.
The most common problem is with IP assignments. One thing first. On the phone under connections > advanced I would turn off WiFi power saving mode, if on.
In Orbi look to see what IP assignments are given to the Samsung Phone. There may be a conflict. See if any device is using 192.168.1.100. That can be a clue to what is going on. Even if when you look there are no conflicts, I would give my phone and your son's Note fixed IP addresses. With 40 devices on your network there may be an issue with tthe Galaxies and conflicting IP assigments.