Ok, so 2 meals a day with approximately 18 of fasting. That should help keep your blood glucose steady. Humalog works for up to 5 hours after injection, so 2 meals means a good 10 hours of effect. If your glucose is dropping while you are fasting (during the 12 hours when there is no effect from humalog) then your tresiba dose is too high and wants to be reduced. As tresiba has such a long duration alterations to dose will take a few days to settle. So small adjustments and patience.
Do you eat low carb? Typically, the lower the carb, the lower the insulin, the lower the variation in blood glucose.
Night glucose levels are often difficult to control. If you could measure during the night, maybe set an alarm for every 2 hours on a night when you won't miss a good night's sleep. (I think many of us have been lured to the libre by the promise of better night time control)