It is not slowing the app startup time.
There are two parts to the Plex app on LG TVs.
The app stored on the TV is a loader app. When launched, it downloads the full app over the Internet. *
The loader app still has the old logo. The full app has the new logo.
Both logos always displayed. It just wasn’t obvious until the new logo was introduced.
* Look at the Plex app version in the LG store. That’s the loader app. Look at the version in your list of Authorized Devices. That’s the full app, currently 5.41.1.