Are the devices connecting to the network? You can check by going to 192.168.1.254 and looking at the list that populates.
Have you more than one router? If a secondary router starts before the main one, devices will get an IP address from it, bypassing the primary router.
Reorder a fibre install, and tell the guy you want a Technicolor FXA5000 modem to replace the Arcadyan one. What is likely happening, is that your Arcadyan modem is having issues servicing DNS requests because its cache is using an older IP address not yet released in cache to do so. Due to ARP not being enabled on Telus's back end for your address, which is meant to solve this issue. This is what is bringing up the intermittent connectivity issues. Arcadyan modems never get firmware updates either, making this problem apparent even more so.