15 lb InvisX, ....... Improved Clinch Knot.
This is the problem.
Switch to a san diego jam, wet thoroughly and tighten it slowly, carefully, and you will have a h3lluva time breaking it off.
When i first tried fluoro i went with improved clinch not knowing any better, had the same probs, would break on hookset or very slight pressure when snagged. Nothing like that since tying SDJ knot (on a bladed jig i use a double SDJ because the knot profile isnt going to be noticeable to a fish on a moving bait). I have pulled small christmas trees off the bottom on 15lb inviz.