Performance issue using materials only

In Substance 3D Painter 10.0.1, my project has essentially Fill layers with Substance sbsar associated to them. There are no Paint layers. I noticed that after a while working with the layers, adding some, deleting others, changing parameters of the Substances etc., performance begins to degrade. Even saving the project, quitting Painter, reopening it and and reloading the project doesn't seem to help. Can someone help identify why this is happening and how to mitigate the problem?

I know that when using Paint layers, performance may degrade because all the stokes are recorded. But here, this is the not the case, I am not using any Paint layer, so why would performance degrade?