Some devices will not pick up wireless network

Hi - I have a lot of wireless devices:  laptops, galaxy tablets, cell phone, TVs.  When searching for my wireless network (in order to connect), the network always populates - I choose it, enter my password & it connects.  

2 device types used to pick up my wireless network & connect with a password - without an issue.  But in the last month, the following has occurred: 

• Nook #1, which had connected to my wireless network for months, all of a sudden would not connect - in the list of wireless networks, mine appeared but it said "not in range."  I did all the troubleshooting steps - rebooted the router, unplugged everything.  Plugged it back in.  Turned the Nook off & on....reset to factory settings.  Everything.  Still - when I search for my network, it's not there.  The network from the dance studio in the strip mall behind the woods of my house - shows up.  Not mine which is in the same room as my Nook.
  
  
• Nook #2.  Yes - I have 2 nooks.  The second one did exactly the same thing.  It had connected without issue.  When Nook #1 had the problem above, I checked Nook #2.  Same issue.  Tried the same things - doesn't work.  Both Nooks are less than 6 months old.  
  
  
• Brother MFC-L8600CDW.  The printer is several years old but has never given me problems.  I do not print every day but yesterday, needed to print something.  It was offline.  It will do this from time to time but I'm always able to search for my network, choose it & with my password, get back online.  Not today.  The network does not show up as an option.  I've tried all the things I've tried with the Nook.

Did something change recently with router settings?  The other devices connect fine - but TBH, I do not want to "forget" my network on a laptop or tablet for fear that it will not find the network again.  

Help.  -Amy