Problems setting CPU speed

[Seeker]

Trying some power reduced things out and ran into an issue, ESP32 WROOM using cmd setCpuFrequencyMhz(240); & getCpuFrequencyMhz(); . Worked a few times trying 10, 40, 80, 240. Then stopped and anytime I execute setCpuFrequencyMhz(240); with any value other than 240 ( ie setCpuFrequencyMhz(80); ) the instruction never returns & program locks. I have looked at a variety of tutorials on this subject without explanation. You comments appreciated.

Al