We're in process of upgrading environments as well as code base to support AEM 6.5.
When I install our project's bundles which use uber-jar 6.5.0 (either apis or apis-with-deprecations type) to a clean AEM 6.5 instance somehow authoring UI of SPA pages appears to be broken: I cannot change edit mode while on a page and Content Finder control is hidden. However all the bundles are in active state, I see no errors in error.log as well as browser's console.
Nevertheless, if I'd change uber-jar back to 6.4.3 everything works fine.
The reason was that we didn't update npm dependencies @adobe/cq-spa-page-model-manager & @adobe/cq-react-editable-components up to latest. This caused SPA Editor fail to make essential ".model.json" calls and thus authoring UI seemed broken.
with SPAs it can be problematic, especially if you rely on undocumented and/or undefined behavior of the UI (which can occur quite often, considering the complexity of both the product frontend plus your SPA and its frameworks on top).
I am not aware of any good shortcut to debug such a situation (I am not a frontend dev), but have to recommend to choose the old-style way of debugging.