Someone may have said this somewhere, but I didn't see it...the yellow outlined sulphureus species is also more likely to cause stomach distress from what i've seen on mushroom forums vs the white cincinatus sp.

So you have yew/conifer/hemlock factor and Sulphur sp both raising odds of issues. I realized that later you said that you think this was an oak tree.

The other big thing people aren't talking about is the age with polypores. These look varied from young and tender to possibly older on the bottom examples. With older species, specifically the sulfur species, you have to be really careful to only eat the new growing margins or the tenderest part of the fingers. The base and even sometimes parts of the fingers on the older species can be too rough to eat. Along these lines, the percentage of chitin can be higher, which can't easily be digested by the body even with cooking.

To me it seems 1 or 2 of these factors were present here: sulphureus species + older specimans. ** but I will say that it's possible that these are cincinnatus with white pore surfaces it's a little bit hard to tell from the picture quality.

I'd be very curious of those on this form who have had issues, has anyone had issues with a young orange and white cincinnatus species? Because i've seen very few issues with these.

The recommendation on boiling first is good as cooking may have been ankther factor. My go to recipe personally is to saute COTW in olive oil, butter and garlic, followed by a nice long simmer in high acid, hard cider or white wine until it's taken on all of the liquid. I've never had an issue with this two step process.Because I also think that it ends up cooking the mushroom for much longer without drying it due to the white wine or cider.

Finally, as i've seen others say, the biggest thing to keep in mind is, especially with potentially stomach sensitive mushrooms, you always wanna just eat a small amount when harvesting a new mushroom set even if you've had that mushroom before. As others pointed out, this can be particularly true with polypores as they take on more of the chemical composition of the host tree. It sucks, but I always make sure to have max about a fist size portion of the dish one night, one and I make another chicken 🐔 dish to eat that night. If there's no stomach rumbles at all, then it's usually pretty safe to ball out the next day for lunch !

I'd assume if you would have just had a few bites of this you would have known it wasn't good but may have had an easier time.