Hello @Luke Bordonaro ,
Thank you for those details. Your issue seems somewhat similar to this one: https://developercommunity.visualstudio.com/content/problem/961208/deployment-center-stuck-on-fetching-deployment-dat.html.
Would it be possible for you to scale your app up and down and check if that helps? Do the deployments on Kudu show any errors?
Regarding the 400s, you might want to enable diagnostics logging for apps in Azure App Service to troubleshoot further.
Here is another similar post with a few workarounds you might want to consider.
Please give these a try and let us know if you still see issues.