Tiny and easy mutator.
Periodically (once per minute) check client render and version and if it is old - notify player, something like this
You are using an old game client. Upgrade to get more FPS and less problems. Google this: OldUnreal GitHub UT99 patch
Install:
Add to mutator list UpdateOldClient.UpdateOldClient (or to ServerActors - preferred way)
Add to ServerPackages UpdateOldClient.
