As it was 5 weeks ago it was installed, I expect you have the separate modem? If so, I'm wondering if here is some way the usage and uptime relate to different things.
The point being that the line stats you see in the HH5 appear to be sent to you by BT. They aren't available direct from the locked modem. Only - the locked modem is actually a router in bridge mode.
I like the alternate universe explanation

. I had to comment though, it was a classic.
My broadband basic info/help site - www.robertos.me.uk |
Domains,site and mail hosting - Tsohost.
Connection - Plusnet UnLim Fibre (FTTC). Sync ~ 59.4/14.4Mbps @ 600m. -
BQM
"Where talent is a dwarf, self-esteem is a giant." - Jean-Antoine Petit-Senn.
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Allergy information: This post was manufactured in an environment where nuts are present. It may include traces of understatement, litotes and humour.