Using this on 8 live sites right now - all vary from each other and none are test sites.
1. Didn't import All in One SEO settings in 3 instances.
2. Won't talk to the sitemap files that is can see and that are writeable or update them - one site only. However, no error message is produced upon telling it to write to the sitemap - either search or news.
3. Doesn't have a way to import from Ultimate SEO.
4. Didn't update the "redirect to clean URLs" option with new data when I altered the site from www to non-www and back. Even after deactivating and reactivating - had to shut off that option.
5. When used with StandardTheme (which is set to integrate your Breadcrumbs plugin) it crashed until I shut off the breadcrumbs in the Yoast plugin. Possibly the fault of StandardTheme - unknown.
6. The plugin is not generating metadata or titles in the case of one StandardTheme install.
7. When I tell it to delete the old information from All in One SEO upon import, it sometimes isn't doing it. No error message generated.
Probably there are good reasons for all of this related to other plugins, the themes, etc. If you want details, contact me - I'm not posting them here.
Those are the only ways I've been able to get this plugin not to work properly, despite complexity and workability elsewhere. Overall I LOVE this plugin - far better than others like it.