We are using Sitecore 9.1.0 and we have defined 52 URLs in applicationInitialization of our web application, which lead to an error: "No owin.Environment item was found in the context." If you have 5 URLs - it does not errors out.
I reached Sitecore Support on this matter and got an answer from them:
I have performed some additional investigation regarding your issue and would like to share the following with you.
Using the setting was discussed with our development team and they confirmed that it had not been tested for Sitecore application.
Thus, we have registered a wish to have this question investigated for future versions of Sitecore.
To track the future status of this request, please use reference number 300564.
More information about public reference numbers can be found here: https://kb.sitecore.net/articles/853187.
Taking the fact that Sitecore does not have any official guidelines on configuring Azure App Initialization feature, the nature of the question you have posted falls outside the scope of the technical support described here.
It means that we are not able to provide you with the requested kind of assistance via the Sitecore Support Portal.
So, this means that usage of appInit feature is discouraged by Sitecore Support :(