This has (sort of) recently happened to me.
I just got over a two-week bout of Covid. I struggle with gut health in general, but (weirdly) while I was sick my gut health was good/normal. I started training again this week, and my gut has been a problem again.
I don’t know if the relationship is causal, coincidental and/or temporary … but I’m trying to sort it out.
Sorry … wish I had something solution oriented to add.