Within Void Linux I have Evince as default PDF/Document viewer, worked fine with Debian and Gramps 5.x so I don’t understand what the problem is here. I can / have to open the file outside of Gramps. Minor issue, I know but having the report open within Gramps is so much easier!
This is not a solution, but a work-around.
Running Gramps on macOS I often see the same problem, when running a text report with output to a pdf file.
Instead I select output to an odt file, and if I need a pdf file, open the odt file in word processor and from there export to pdf.
Thanks for the reply @csam !
You’re right, it’s a possible work-around But saving to pdf is not the problem. So I can open the pdf file from the dedicated folder. I’m just a bit lazy and got used to gramps opening the file right away…