I have used the improved clinch for over 45 years and I don't remember it ever slipping until last week. Now every time I tie one, it slips. Old line, new line, it doesn't matter, it worked with both before last week.
I have to be doing something different, but I just can't figure it out. It's not so much that I can't use another knot, because of course I can.
I'm just perplexed.