Foliage Instance Unloading

Hi experts,

I’m seeking some assistance with foliage painting. When I paint foliage on my landscape the instance seems to automatically unload itself. Sometimes it will paint correctly, however when I let go of the mouse, most (not all) of the foliage unloads.

I’ve spent a day trying to troubleshoot this issue and I really don’t want to just go pressing buttons, for fear of creating another 6 problems.

World Partition is enabled and all cells have been loaded via the World Partition Editor. I have tried the pinning trick which gives me access to the instance details, however the instance then vanishes from the Outliner.

Any suggestions would be great.