VDSL Disconnects at night sometimes...

Hi, Remote Office VDSL/FTTC connection with very stable line (BT Business)
8. Data rate: 20000 / 79995
9. Maximum data rate: 29149 / 98568
10. Noise margin: 12.0 / 11.1
11. Line attenuation: 9.1 / 9.7
12. Signal attenuation: 8.9 / 9.7

can sometimes disconnect at night, what causes this? usually around midnight, it re-syncs and shows this in the hub logs,
last night it was off for 3 hours from 23:45-03:17, is this down to BT doing upgrades?