I mean, bugs are a part of all software. Stability is about reliability. That if you boot up your computer you are less likely to spend the first hour or two troubleshooting unless you just did a major upgrade. I’m not saying Arch is unstable, just less stable.
Anytime there is an update, files are often deleted during that process so they can be replaced with new files or because those files are no longer part of the new version being installed. If an error occurs during this process, it is possible that an application will appear not to be installed because it’s broken.
Anyway, most software does at least partially “uninstall” when it is updating, so if the install fails, then it’s always possible that an update will have uninstalled something. That’s just updates regardless of operating systems, package managers, etc.