Hey folks - Just to loop back here, through a couple of threads we've identified a really obscure bug when loading apps without their uuid included the URL. This can occur if opening apps by URL from other Retool apps or opening apps from a static place like your browser's bookmarks. Lots of things can contribute to bad performance, but this specifically results in the page hanging before any queries are run (either completely blank or only showing the spinner animation).
We're following up on this as an incident on our side, but a workaround in the meantime is to either include the uuid in any links to apps or just set a custom URL in the app settings (simply setting that avoids the issue entirely for anything linking to the app).