I experienced this with QV 8 and QV 10 quite often and now with QV 11 very rarely. I think the reason for this behaviour is that you hit any limits regarded to available Object-RAM, timeouts by the calculations and maybe an issue with the caching-engine from qlik.
At first I would take a look on the used dimensions/expressions and trying to optimize them in combination with possible changes on the datamodel - to avoid calculated dimensions, aggr-functions, nested if-loops and maybe some more.
Hi Marcus and thank you very much for your swift reply!!
I think you must be right there. There is a LOT going on in this qvw; it's a real hog. I will do the optimalisations you recommended! There are some quite complex set analysis functions going on here, and some nested ifs; the latter will be the first to go..