Only added the modem for them last week, but that did fix the evening resync issues they had. They had tried support due to the resync interrupting streaming, who gave a long set of notes on splitting Wi-Fi channels - but support seemed to have overlooked that streaming device was connected via Ethernet.
Will check in during lunch break and if not fixed itself will get them to sit in plusnet queue.
Could they have changed their PN member centre password?
This will also change the PN CHAP password, requiring the new password to entered into the router.
They had themselves bypassed the modem this morning and things worked again.
Swapped back to the Openreach modem in the way and bobs your uncle all fine now.
So its not really clear what issue was, logs suggest a router restart at night, possible firmware upgrade so maybe things were just confused.