Unless there is someone here who is a very knowledgeable user of KiKit (it’s a Plugin not part of KiCad) then your best option is the Author’s GitHub pages . . .
I had the same issue recently. For me it was because of their recent change, that you can no longer paste the panelized board in the file you currently have open. Well you still can, but it crashes at some point, when it is around 99% finished. Then it looked like this. Creating a new PCB file and selecting this new file as target, resolved that issue for me