This is an issue I have come across deploying Apps in non-English PWA site collections, while the App page loads clearly something is wrong, see a screenshot:
If you press F12 in IE or Chrome and open the console you will see errors like the following:
Failed to load resource: the server responded with a status of 404 (NOT FOUND) https://*****-1edc3a4f15d104.sharepoint.com/sites/testfi/_catalogs/theme/Themed/634341C6/corev15app-DDE41C8D.themedcss?ctag=0
From my testing this issue only came up in the last few months but fortunately there is a fix.
The problem appears to be caused by the provisioning job not deploying certain resources, fortunately this can be fixed by modifying the Alternate Language settings of the site collection. Simply selecting English as an alternate language will install the required components, and better yet when you then proceed to un-select English from the alternate language options the required resources remain and the issue is fixed for good.
Steps to correct issue
- Open Site Settings in your PWA or other site collection where the App is deployed.
- Open Alternate Languages, and select English as an alternate language.
- Save the settings and wait for the changes to apply.
- Now opening the App should work without display issues.
- Finally if required repeat step 1 and 2 and de-select English to restore the previous setup (while keeping the fix).
HTH,