We do normal probios during abx and about 3x the normal dose following abx.
I haven't heard of probios & diarrhea - that level must have to be super high - or even maybe even a unique allergy to the specific probio.
With the devastation of the GI by the abx I wouldn’t worry about too many probios. I would worry about yeast much more (not having enough good bugs in there to hold down yeast.) CF results in intestinal inflammation. probios have been proven to reduce that inflammation. We do probios all the time.
Probios help boost the immune system too - maybe this might be something that can really help you.?
(Klaire Labs has even designed a probios to take when on abx...) http://www.klaire.com They have a lot of great info in their catalog.