Hi, yes, there were improvements to this in V10 and V11:
From V10 changelog:
Improved performance when rendering with masks
In cases where the user includes just a small object and the rest of the scene is not rendered we get up to 600% speedup. In non extreme cases it leads to around a 10% speedup
From V11 changelog:
Bucket rendering - improved decision when to revert to random pixel rendering based on render regions and rendering mask.
My suggestion is to update to Corona 11 Hotfix 2 -
https://corona-renderer.com/downloadThen test your case, and if you are still observing a slowdown, submit a new ticket at
https://support.chaos.com/hc/en-us/requests/new