NASA reports that two recent, known issues caused Mars 2020 Perseverance to put itself into “safe mode” — the first, is that immediately after launch, the proximity of the spacecraft to Earth saturates the ground station receivers of NASA’s Deep Space Network. Mitigation strategies included de-tuning the receivers and pointing them slightly off-target from the spacecraft, to bring the signal within an acceptable range.
The second was a transient event involving the temperature of the spacecraft. There’s a known differential between the temperature at the center of the craft, and the temperature near the skin. As the Earth moved in between the Sun and the spacecraft, the differential dropped, causing the craft to go into “safe mode.”
