I suspect that you are uninstalling the "Akeeba Ticket System" component instead of the "Akeeba Ticket System package" package. This will not work as it will leave behind the plugins. If you have left the plugins enabled, like the system plugin which checks for emails, they will get triggered by Joomla, they will look for the now missing component and they will fail. This is what causes the problems.
Unfortunately, this is a shortcoming in Joomla. You cannot tell it that the user should not try to uninstall one extension instead of the entire package. You cannot have it stop the user from doing so either; from the perspective if the installation script -which also gets triggered during uninstallation- there is no way to know if the user is trying to uninstall just the component or the entire package. So we have to trust that our users will not try to uninstall the component instead of the package.
Before you say that we should solve this; our hands are tied. We are forbidden from even using a custom installation, update or uninstallation method which does not involve Joomla's extensions manager in any of our extensions. If we do so we will be immediately expelled from the Joomla! Extensions Directory (JED). Not for just the offending extension, but for all our extensions. In other words Joomla! forces us to use its own code to handle installation, updates and uninstallation with all the problems that entails.
Remember that I don't say this because I'm too lazy or too ignorant to implement anything better. These words come from the guy who wrote the first ever live update checker on a Joomla extension (back when Akeeba Backup was called JoomlaPack in 2007) and the first ever on-line, single-click Joomla extension updater (back in the early days of Akeeba Backup 3.0 in 2010). My code, Akeeba Live Update, was working better than Joomla's but I had to discontinue its use because I'd get kicked out of the JED. My extensions were packaged as components which handled the installation / uninstallation of plugins etc. Unfortunately, I had to discontinue that practice as well for the same reasons, even though my solution worked far better than Joomla's "package" extension type. I had the solution, they were deployed for years, they were battle tested, they were stable and I had to stop using them because someone basically came up with a decree "use Joomla's own code or you get the boot".
Sorry for the tangent (or rant, really). Please just uninstall the "Akeeba Ticket System package" package extension. The same applies with all Joomla extensions shipped as "package" extensions, i.e. virtually everything except single module or plugin extensions (if there are still any left). In the Extensions, Manage page click Search Tools, click "- select type -" and choose "Package". These are your valid uninstallation targets. Anything else you shouldn't uninstall unless explicitly told so by its developer.
Nicholas K. Dionysopoulos
Lead Developer and Director