Use case : We were trying to deploy the solution from dev environment to UAT but Sitemap changes were not moving to UAT.
Solution : after RND we noticed that App extension for that particular app were not present in the solution
Then we tried to add app extension and it is working
To add app extension
Go to solution-> click on the component -> client extension and add extension for your app.
Now Save and Publish. And try to deploy the solution.
I hope this helps you while deployment of apps.