Brand new coils may have a cotton like taste to it this is also known as a “dry hit”, to avoid this you must ensure you coil is properly primed and always start breaking in a new coil at low wattage. If the coil still does have a cotton like taste to it, it could very likely be due to the E-Liquid that you are using. Any E-Liquid above 70VG will cause factory coils to dry hit. In this instance lower your VG content.
If you still insist in using E-Liquids that contain high VG content, you should look into rebuild-able atomizers as factory coils arent capable with E-Liquids that contain high VG.