The server is liable to create the following errors.

504 Gateway Time-out
nginx/1.1.19

If you do a big track edit, it is almost certain to destroy your work. I was creating a new (ie structurally corrected) 13CD release within a release group. The problem is likely that the server had to deliver a large number of recording suggestions for me to select. It could not do this within the time-out. I could not get to the "recordings" tab, or anything beyond. I could navigate to the earlier tabs ("Release informtion", and so on).