My wife and I had the same issue many years ago. Chardonnay’s, particularly those from the US and Australia, would give both of us splitting hangover headaches. This persisted for some time, and for decades we were ABC wine buyers and drinkers.
This stopped a few years ago, and currently, we probably buy more Chardonnay than any other individual varietal. For no reason, the hangover headaches have not returned.
I have no idea if this is related but I’ll toss it out there.
Back in the late 80s, when I started making vinegar from leftover wine,I tried to make vinegar from a bunch of California chardonnay. The stuff just wouldn’t turn. Ever, even with a starter.
I assumed it was because of the sulfite levels in those days. I made other batches of vinegar from other types of wine and never had a similar problem.
Brain variation.
Depending on the producers in that collection, there are a couple additives such as fumaric acid that will prevent bacterial growth that are supposedly mainly used by very, very large wineries that do not allow ML fermentation to occur. Perhaps a little bit of that could have gotten into the mix, preventing the bacteria to grow.
I don’t think the usual amount of SO2 that the average Chardonnay contains would be enough to inhibit acetobacter when added to the vinegar mother-especially if the bottles had some age on them.
F
Probably a variety of factors: generally Chardonnay is pretty high in alcohol vs other varieties in a given region; it often sees full malolactic which, especially with native ferments, can deliver high levels of histamines, biogenic amines etc.; and on top of that it’s often hit with pretty high sulfite doses.
Maybe you can drink more chard in a sitting than drinking a red hence the hangover.
Sorry if I missed this in the thread, but we are talking about single variety drinking sessions? I’d only Chardonnay etc.
A mixture of white and red wine over an evening without copious water and or food is a sure recipe for a headache. Chardonnay would often be followed by other wines which is why I’m asking. Of course then how can one ascribe the headache to anybparticular wine(s)
After several years of no chardonnay induced headaches, they returned with a vengeance after particularly good Chablis. The next day I purchased an identical bottle, and in the name of science, will see if the condition can be replicated.
Consider it the price of pleasure and focus on the joy before the headache.
Experiment: After Chard drinking, use Afrin a few sprays in each nostril at bedtime and see if that affects your result!
I don’t think there is any scientific reason to believe that mixing per se makes hangovers any worse.
People probably get the idea because nights where you have several kinds of wine and/or booze and/or beer just tend to be nights you drank a lot more.
And then the idea has become popular so there is confirmation bias. “I have a hangover — it must because I had different kinds of drinks last night.”
Other than placebo effect, I highly doubt the hangover for half a bottle of white and half of red is any different than a whole bottle of one or the other.
Way back on on the P board there was a really good and thorough post by a doc about things that can cause or contribute to hangovers. Several really interesting things were in there that we don’t often think about but I don’t recall mixing of different types of wine. I don’t think I can help the OP here but I remember one of the culprits being cheap wine because it often includes things other than grapes (aka MOG). Things like bugs but more specifically bees and maybe spiders, which may contain something poisonous, that don’t get sorted due to labor/machine costs in cheap wine.
Along these lines I was thinking many Chablis could have more herbicides (organic or not) than some other regions because it is kind of a tough region to grown in but I think the OP mentioned trying chards from several regions and still had the same issue.
I ended up switching from beer to wine a long time ago because after years of enjoying beer something in me changed that caused a hangover-like feeling that lasted up to two days after as little as a single beer. Never quite figured out what it was but pretty sure it is the barely after finding a similar effect with hard booze made from grains.
Another anecdote
Back when the world was young and I was up at university, I was at an afternoon party where they served a gin based punch. At the end a few of us were invited to stay on for an after party, as it were, where they poured champagne (and some finger food). Second worst hangover of my life. 
Perfect illustration of how many people would use confirmation bias and say that mixing drinks was the problem, when it pretty obviously was just how much you drank that day.
Another one you hear all the time is “I drank wine all the time on our vacation in Europe and I didn’t get headaches because they don’t use sulfites.”
You may be right about about anecdotes. It wasn’t confirmation bias though - I was quite unprepared for the results.
Yes there was a fair amount of consumption, but there were plenty of other occasions during student years when consumption would have exceeded that, with much less dire consequences. I do not, did not, generally mix drinks - the problem that day was I didn’t know there was going to be a part II, or the risk I was running.