The Hubs do, the very odd time, throw a strop and reboot themselves.
Try a 60 second factory pinhole reset as below;
Remove any ethernet cables from the Hub and hold the pinhole reset switch for 60 seconds. Do NOT reboot the Hub, just let it do it's thing. Note you will need the passwords from the bottom of the Hub afterwards, so make sure they are legible.
If this fails, maybe the Hub is faulty and will need replaced?
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