It seems that I have started cataloging my experiences with the rather common Layout Run Error in ExtJS portals, as it's one of the most frustrating errors to fix. Previous editions include:
This time I came across another rather simple scenario where I was troubleshooting something unrelated and in process was setting "hidden: false" on various components, in hopes of divide-and-conquering my way out of the issue.
Sure enough, got a "Layout Run Error" when I set one of my components as hidden. There was nothing particularly special about it - a Container extension sitting inside of another Container with "auto" layout. At that point I commented out my Container instead of setting it hidden: no more layout run error!
I decided not to spend time figuring out why this particular container didn't like being hidden from the very beginning, especially considering this is in context of rather stale 4.2.1 ExtJS codebase. Nonetheless, the lesson is: even a simple act of having component declared as "hidden: true" initially can be enough to cause Layout Run Error.