I have a problem with theme customizer. When I try to use it I get “Non-existent changeset UUID.”. I’ve checked the obvious places (siteurl vs home setting, memory is set to 128M, cookies cleared, etc.), did not help. This is a multisite installation with GP Premium. The funny thing is that a twin blog with exactly the same plugins enabled works without a problem. Any hints on how to debug? WP_DEBUG = true doesn’t really show anything.
I think I found the cause of the issue. My provider has set up a transparent proxy in front of my host. Once I got excluded from it, things started to work again. Interestingly enough the other wordpress was on the same IP and it worked without any problems.