Unable to change themes

I have a site on a development server. In the past, I had a custom theme for All in One. I updated the plugin, and had some error occur, so I deleted the custom theme I had (which originally was stored in /wp-content/themes-ai1ec/), and then deleted the All In One plugin entirely. and re-uploaded all the files from a fresh download of the plugin.

However, even though I did all of this, when I choose any theme other than the default, the plugin tells me the one I’ve selected is active – but when I look at the front-end of the site, it’s still the default theme.

I’m not sure if I’ve messed something up in my install. Is there a way to reset the theme option without resetting the entire plugin?

https://www.ads-software.com/plugins/all-in-one-event-calendar/