The error that can be seen in the initial post, “The request could not be processed in a reasonable amount of time” indicates that some of the views that the application is querying are not indexed.
This could cause the replication requests to time out as well.
If it’s a new installation, you should wait until the views are indexed before using the app.
If installing via horticulturalist, there should be logs indicating the view indexing progress, otherwise you can check the active tasks yourself (1.2.1. / — Apache CouchDB® 3.3 Documentation)