I would actually suspect the banana. I can't tolerate even the ripest bananas, as much as I wish I could. And I don't know many on this diet who consider them safe
And one other thing that you may or may not find useful: I never mix coconut milk and fruit in smoothies, doesn't work in food combining for me, gives me a stomachache right away. I call it a fat and sugar bomb as it is ingested so quickly. BUT, that is also just MY body! You might be totally different.
I like fresh nut milks and fruits, also coconut water and fruits. And I do make coconut ice cream with some fruit, but it is eaten much slower (and in much smaller portions than a smoothie). I made a vow with myself to never drink another coconut milk based smoothie with fruits. Again, this is what works for me. Others out there say the opposite!!
I also live on smoothies, and usually replace 2 meals a day with smoothies. I just no longer make them with fatty coconut milk. Some of my favorite smoothies:
Homemade almond milk, strawberries, dried apricots
Homemade walnut milk, pear, rosemary, cinnamon
Coconut water, pineapple, basil
Homemade walnut milk, cacao, dates, baby spinach
Homemade almond milk, matcha green tea powder, mint, figs
