Cannot Edit a Child after creation

I have a created a child table and added fields to it, I thought I’ll reformat it later. But it is not saving the changes.
How to fix this?

v15 or dev?

this is it.

Please check with the stable branch, because, in the dev branch, everyday changes and developments are added.

we checked with v15 stable, and it’s working properly. Will check later for dev.

Okay, thank you.