Can confirm, most smok coils are juice thirsty. the X4 coil i remember was pretty good on juice use, i vaped it around 40-50W. Then i replaced with the T6 that came with it. Loved the thick delicious cloud it made, I use mine around 70-75W. Sucks down about twice as much juice if not more than the X4 coil.
As for the burnt coil taste. It could either be the coil is gunked up with the juice your using, or the vape pen being unregulated might be going a bit too hot for the coil installed, which would be hard to do with a smok coil as most can handle higher wattage than the pen would start off at.
It sounds like to me that you ended up burning the cotton wick around the coil. I had the same problem when i accidentally didnt have my stupid touch screen on my GPRIV locked and my hand jacked it up to 220W. Was a sharp painful inhale then after that a burnt taste that went away once i swapped coils. It also started to leak out the bottom (burned cotton not absorbent)
My advice is to change the coil. Figure out what wattage range the pen utilizes. You might have hit it too much and the cotton dried out and started to burn. Once you burn the cotton its nasty burned taste until you swap coils out. Look up what coils come with the pen then replace with those, a 5 pack shouldn't cost you more than $20 and should last you a month or two depending on the juice you use gunking them up over long term use.