Not surprising in the least. Heightened caffeine is not good.
Period.
When mtn bikig in the 90’s I discovered a gel which contained guarana, which had similar effects to Red Bull. I had read syudies on the nature of guarana and the fact that it was not safe and I stopped taking it.
The problem today is that it is en vogue to take this garbage, and not even for mtn biking. Just for everyday drinks!
“Heightened caffeine is not good.”
Maybe not, but my mother has had 6-8 cups/day for the past 80 years and is more able than most people half her age.
I drink one cup of coffee in the morning and IF I drink a soft drink during the day, it is caffeine free. I’m glad to see that more and more of the popular drinks are caffeine free.