14 May. (57217.100000) PPP LCP Send Termination Request [PPPoE PADT received]
That seems to suggest that the HomeHub received a request from the cabinet, though you could read it as reporting that the cabinet has received the request from the HomeHub. Whoever designed the logging system could have done a better job.
There are lots of other threads discussing these annoying log entries which could happen for differing reasons. The HH5-A seems flaky in this area. It would be interesting to know if you still had the same problem when using a separate white Openreach VDSL modem with the HH5 just as a router, or even a totally different brand VDSL modem-router.