When I open my writer document containing mail merge fields and click on the print icon, a window opens stating "Your document contains address database fields. Do you want to print a form letter? If I click on the "Cancel" button, nothing happens and libreoffice doesn't crash. If I click on the "No" button it takes me straight to the Print Menu and I can close that and libreoffice doesn't crash. However, If I click on the "Yes" button it takes me straight to the Mail Merge Menu and it doesn't matter whether the Output is to "print" or "file" or whether I subsequently click on the button "OK" or "Cancel" Libreoffice crashes. See Crash Report: 12c4d5ad-204a-4b61-bc45-f61148615436
Looking at the crash signature, it looks like a dupe of bug 117824, which is fixed in master, the upcoming LibreOffice 6.1 and 6.0.6 *** This bug has been marked as a duplicate of bug 117824 ***