Totally understand as I've had the same happen. Especially when pushing the fasting hours a bit longer.
Since I started sticking to strictly 16/8 and upping fat intake with especially first meal it has gone a lot better in the past 6 weeks.
Have to find what works for you and like you mention, it must be sustainable.
@APoc184 , do you mind sharing examples of fats that you're eating please? I seem to be struggling with this a bit.