LoopMash FX doesn't load up

Virtual instruments Virtual Effects and Add-ons
2

While we do not officially support 10.10 yet, have you tried using the Steinberg Application Installer Tool to reinstall?

https://www.steinberg.net/en/newsandevents/news/newsdetail/article/official-letter-on-yosemite-update-2837.html

Personally, I would suggest staying with 10.9 for the time being.