Vitamin fizzy / soluble pills can cause it for some people.

I narrowed it down to grapefruit. At least that's what I suspect. I avoid them now.

grapefruits should usually help, as they're high in citric acid.

most citrus fruits help to reduce kidney stones, but not grapefruit. grapefruit has different weird interaction with medication and does increase risk of kidney stones, contrary to other citrus fruits.

https://www.webmd.com/diet/foods-high-in-oxalates

I don't know what to believe any more because that article says kale is a low oxalate food, but https://blog.swedish.org/swedish-blog/kale-causes-kidney-sto... says the opposite (and was on the list I got at discharge)

Nutrition science does change at a surprising rate. In case of doubt... drink plenty of water!

As far as I understand it, the interaction of Grapefruits with for example statins is because it has Furocumarine, but that isn't unique to it. Other citrus fruits have it as well. It's just that Grapefruit isn't as sour and it's consumed in much higher doses compared to say lemon juice.

If you get one, try to catch it and have it analyzed. I had a calcium oxalate stone. My urologist suggested adding some milk to my coffee (I had been drinking it black). Haven’t had another in 10 years.

You have to get your stones analyzed and they'll make suggestions based on what the composition is.