Hello,
Firstly, the WoodMart Core plugin wasn’t updated to the latest version (1.0.35) on your Site which we have updated now.
But it seems that there is some Customization done in your Child Theme which is causing the conflict because like you mentioned & we have confirmed it too that it is working fine under the Parent Theme. So, it is not an issue at the Theme level but due to some Customization conflict.
On our Test Site too, the option is working fine. So, you need to once reconsider the Customization done in the Child Theme.
Best Regards