"GUI not loading" is one of the most common support requests we get, and it's usually caused by some PHP notice interfering with the REST API output (JSON parsing fails on the client).

We should improve the situation and load the UI even if there are some notices or other non-JSON output in the response. There are two levels on where we could improve things:

1. On the server side. There are tricks with output buffering available.
2. On the client side. This is probably where the focus should be because in the end, client must deal with the malformed response.