I have the feeling this happens since the beginning of IX1. I’ve never been able to really use a initial state for an element that should be masked. It will always flash appears on load. So I design their initial state. It’s less convenient for maintenance. For really hiden element,s difficult to edit, I make their content a symbol and gather all those symbols on a dashboard page, so editing them is easy.
Sorry I don’t have a proper solution but I don’t think there’s one.
I disabled the Rocketloader script from loading on my server.
The script was making all .js load in async mode, which is good for speed, but not so good for rendering.
I guess you have to choose between speed or design…