The old client injected too early, allowing Psyonix’s anti-tamper (Denuvo’s anti-cheat lite) to detect the hook. The "fixed" version waits until you are in the main menu, then performs a staggered injection over 3–5 seconds to avoid detection.
“Yeah its been a thing for awhile... you can totally hack the titles in... but nah, Psyonix are indeed investigating the issue.” Reddit · r/RocketLeagueEsports · 5 years ago
If a file is named Miku_Client_Fixed_Titles.exe and is under 10MB from an unknown source, treat it as highly suspicious.
Even with the "fixed" version, Psyonix can detect you via: