provider for google calendar not 'providing' again..

[pete of ebor]

Been using TB with lightning and provider for google calendar for ages, years in fact with very few problems. Today, Provider for GC has started asking me to log into my google account every time I start TB. If I don't log in, my calendar is blank. Every time I log in again, I immediately receive a warning email from Golgle that someone (presumably me) has just logged into my account. Provider never used to do this. Anyone else got or had this problem, and know how to fix it ?

Thunderbird 52.9.1
Lightning 5.4.9.1
Provider for GC 4.4.1
Win 10 64 bit.