Yes, all recent releases of QlikView (11.20, 12.xx) are compatible with Windows 10. See the System Requirements document.
Yes, there are known issues. See the Release Notes that accompany the particular QlikView version you are using. It has a separate section on "known issues".
Yes there are bugs. QklikView is complex software made by humans. Bugs are reported almost every day. If you want to know which bugs are still unresolved, contact Qlik Support and present your problem(s) to them. Don't forget to mention which version (including SR number) you are using.
AFAIK only Partners and (Enterprise) Customers can contact Qlik Support. The procedure used to be that even customers had to contact their partner for first-line support, before contacting Qlik Support. But I'm not sure that requirement still applies.