Interestingly my current sensor started (~8 days ago) reading low (by 4mmol/l, but non-linear and very close at low BG so could be calibrated with just a gradient change), then moved to reading a bit high (~1.5mmol/l - again calibration fine), and is now back to reading low (2.5mmol/l - but can't be completely fixed with calibration as it's an offset offset, i.e. the line has been shifted completely.)
Unusual, they either stay on one side, or eventually head back to being roughly correct. Maybe it's to do with the weather, who knows.
What I was getting around to saying, is that certainly for me and with the libre(1/2/2+) I do finger prick calibration checks every day to make sure I don't end up running high for extended periods by trusting the CGM (high because - you'd notice if actual BG is lower than the sensor and they just almost always tend to read lower than actual BG in my experience.)