Weird: can tolerate ascorbic acid but not buffered?!

Hi! I have major health issues mostly stomach related. They're all in a post titled 'help me I'm starving'. Anyhow, I used to take quite a lot of vitamin c in the form of ascorbic acid, and it really made no impact on me, neither positive or negative, even at high doses. So I decided to try buffeted vitamin c (calcium ascorbate with rutin, hespiridin, and bioflavonoids), which I read is better and easy on the stomach ...holy cow ...that stuff gave me the WORST burning in my stomach and non stop diarrhea for five days! I took 500mg tablets, one in the morning and one at night, by the same night I was suffering. Maybe it was o e if the other ingredients in it? Or was it just die off reaction? But why would die off burn my stomach? Even when I ate my stomach would burn.
I thought buffeted was meant to be easy in the stomach?!
Any thoughts? Was it die off? I'm scared to take it again.
Thanks Tweet