I'm getting a timeout (504 gateway timeout) when I try and preview a Print/Merge Document with more than 40 contacts in it. First attempt was with a Membership search, but also tried turning that into a group, using a Contact search and removing the membership related tokens - same problem.
Whilst I can't remember the details, I am sure that I have done much larger print/merge documents before (on earlier versions)
Using Civi 5.11.0, WordPress 5.2.2