Every time i log on on retail, Sexy Map loads the Classic version. The only solution I've found is reinstalling the addon with the game opened and then reloading my UI. I got this issue since Classic launch. Thanks.

Use the Twitch client to manage this for you.
If you already are and it has installed the wrong version, make sure you exit the Twitch client completely and re-launch it so it can self-update.
After doing that, with WoW closed, uninstall the addon and install it again in the Twitch app.