I am trying to add three distributions. One of them is taken from an histogram directly with RooHistPdf, for the others I have a formula and I have simply implemented it.

I found out that a divergenze at zero appear when I sum up the analytic pdfs with the pdf from the histogram. I have prepared a macro that you can run.

Thank you for the question and the nicely layed out reproducer, this is extremely useful for us! I will invite @jonas to take a look so we can understand better the situation.

I am using 6.26/10.
Just now I have found the issue: I changed the definitions of the analitic distribution adding an absolute value. I do not know why the divergence appear only when I try to add the analitic + the histo derived distribution, anyway now the problem is fixed. However, the problem looked like this: