Nkristie

Apple networking gear should be replaced. WiFi extenders are not a good practice in most cases. It's 10x more stable to wire and put in WiFi Access Points. 
Put in a recommended router. Put in a few access points in place of the extenders. Configure the DNS on Control4 products as mentioned above.
I totally agree that all your issues sound like they're network caused. These steps should help all your network function better and your Control4 run a ton better.

First, don’t use the Xfinity modem as your homes router.  Put it in bridge mode and use a good router to run the show.
All your problems point to network problems.  Most likely DNS is configured wrong either on the devices themselves or the network.
DNS should point to 8.8.8.8 and 8.8.4.4
 
Cant speak for your installer, couldn’t tell you how knowledgeable they are.  Wish I could get $200 a hr for mediocre work though.  Crikey!!
 

Thanks all! The previous owner has only directed me to the dealer when I inquire.
I live north of Houston. I can see Control4 is option in my network options, but it’s password protected. 

Thanks! Calling today! The pre ious owner is unhelpful and the dealer they had install it is not calling me back!