When do you take your Gliclizide? If you are taking a dose in the morning then not eating this could be why your experiencing lows and sudden fast drops - are you actually in hypo territory when you test at these time - 3.9 or lower?
When I was on Gliclizide as it’s a hypo inducing drug I would need to eat within 20 minutes of taking it.
There’s no rule that you can’t have a snack at night if you want to, I used to have a small 10g carb snack about 2 hours before bed when I was on Gliclizide, now I’m off the meds I still have a snack but it’s around 2g carb.