Please help as Tech support hasn't 

I have issues with my main deco randomly dropping wifi internet. Light turns red during. 
 

I have fiber broadband with modem set in bridge mode and wifi off. Problem happened even when wasn't in bridge mode and wifi on. 
 

Routinely, with more and more occurrence lately, I will get notifications my wifi has disconnected. Last seconds to minutes and then notifications it has reconnected. Alert is from alarm system but all devices disconnect and isn't device specific.

modem lights are fine during this time. Hardwired devices to modem still work with no issue. I have Hue light bridge connected to main deco and its lights don't show issue when disconnect occurs. 
 

my connection is as follows. Modem > Main XE5300 > two xe5300 satellites.  Also....modem has 4 ports. One for lan into deco, one for lan into 8 port switch (only three hardwired connections but devices on here and there), one for lan into Apple TV, one for lan into ps5.

any help with suggestions or fixes would be greatly appreciated!! Thank you