We have installed and activated the storefront theme in our local site and tested with “woo custom stock status” plugin.
It seems all the customisation options are working.
Can you please check any other plugin cause the issue?
Please check the following demo video
https://drive.google.com/file/d/1faAEWVkGj1u7otIxdyhdnDXsarAiRclA/view?usp=drivesdk
Thanks