we are also experiencing very slow response from nPrinting Designer.
We've got nPrinting 17.2.0 with Qlik Sense 3.1.
nPrinting Designer takes a long time to open when I click "Edit template" from Report Overview and report preview also takes a few minutes to generate even when working with very small apps and have very few details on nPrinting report. Sometimes it hits timeout.
Did you manage to solve that problem or have any clue how to fix it? I'm probably going to register a case on tech support.