Orange pi 0 heats up and then freezes

Hello,

We are using Orange Pi Zero with  Armbian Bionic with Linux 5.4.20-sunxi armv7l GNU/Linux

we are facing a problem, our orange pi heats up some time during processing and then freezes.
We can ping the devices, but ssh stops working and all the application don't respond
We followed the suggestion in thread: https://forum.armbian.com/topic/7848-mysterious-freeze-and-overheat-of-orange-pi-zero/?ct=1587196371&_fromLogin=1
But output of "armbianmonitor -m" is as below
Stop monitoring using [ctrl]-[c]
Time        CPU    load %cpu %sys %usr %nice %io %irq   CPU  C.St.

11:19:37: 1008MHz  0.18   6%   1%   4%   0%   0%   0% 76.4°C  0/4
11:19:42: 1008MHz  0.17   3%   0%   2%   0%   0%   0% 75.1°C  0/4
11:19:47: 1008MHz  0.15   3%   1%   2%   0%   0%   0% 75.2°C  0/4
11:19:52: 1008MHz  0.14   4%   1%   2%   0%   0%   0% 74.8°C  0/4
11:19:57: 1008MHz  0.13   3%   0%   2%   0%   0%   0% 75.3°C  0/4
11:20:02:  480MHz  0.12   4%   1%   2%   0%   0%   0% 75.7°C  0/4
11:20:08: 1008MHz  0.11  14%   3%  10%   0%   0%   0% 74.8°C  0/4
11:20:13: 1008MHz  0.18  15%   1%  13%   0%   0%   0% 78.7°C  0/4
11:20:18: 1008MHz  0.41  13%   3%   9%   0%   0%   0% 79.1°C  0/4
11:20:23:  480MHz  0.37  21%   5%  15%   0%   0%   0% 76.8°C  0/4
11:20:28: 1008MHz  0.34   5%   1%   3%   0%   0%   0% 75.0°C  0/4
11:20:33: 1008MHz  0.32   4%   1%   3%   0%   0%   0% 74.5°C  0/4^C

As you can see there is a flip in frequency for a very short time, not enough to cool the CPU
Also the content of /sys/devices/system/cpu/cpufreq/ondemand/sampling_rate is 200000

So what could be the reason that the device freezes.

Thanks,