To build on Dave's reply in the light of the new hub being sent to you:
The usual reason why rebooting gets WiFi back is that the hub's WiFi settings, be AUTO, the reboot results in the hub choosing the least congested channels. It can get quite complicated though. If you've got the 2.4GHz band set int o 'NB' mode, then the two bonded channels may not be interference free. Also your neighbours will get into the same pickle and it's a merry-go-round.
To delve deeper, if as an experiment you switched off the 2.4GHz radio and you just worked for a while on 5GHz, does this still happen?
Seph - ( DEFROCKED - My advice is at your risk)