CPU Frequency Behavior Changed over 2 days

> lsb_release -sd
Ubuntu 20.04.2 LTS
> uname -rpo
5.8.0-59-generic x86_64 GNU/Linux

Motherboard: Gigabyte TRX40 AORUS Xtreme
CPU: AMD Ryzen Threadrippt 3970X

I do not have gnome or Ubuntu desktop - command line only.
I have ondemand as scaling_governor

Two days ago, I ran prime95, small fft for an hour, monitoring cpu freq and temp.
  freq /sys/devices/system/cpu/cpu*/cpufreq/scaling_cur_freq
  temp /sys/class/hwmon/hwmon?/temp?_[label,input]
I saw freqs up to 4.5 GHz and temps up to 94 C.

Today, I changed the case cooling and tried to repeat the measurement.
I rebooted in the process.
I ran prime95, small fft for an hour, monitoring cpu freq and temp.
The freq stayed around 3.5 GHz and the temps at 71 C.
I do not think I changed any configuration.

Any idea where I can look to restore the two day ago performance?