Hello everyone
In general, the cause of the problems was a physical malfunction of the computer.
I had a second computer that was completely identical to the problem one. I installed pfSense on it from scratch and transferred all the settings to it manually. I haven't installed any additional packages yet. Since then, there has not been a single unplanned reboot, the system is completely stable. It's been over two months. I plan to reinstall the necessary packages in the near future and continue monitoring.
After transferring the system to a new computer, I decided to experiment with the old one.
To begin with, I decided to completely reinstall pfSense with SSD formatting. I booted from the LiveCD and started the installation. I didn't even have time to rebuild the disk, as I received an error and a reboot. I thought that the SSD was faulty (although his SMART is fine), I replaced it with another one. The error was repeated. That is, it's not about the disk or RAM, because I changed it earlier. But in the end, after 3-4 attempts, pfSense was still installed. But after standing on for a while, the computer spontaneously rebooted. Then again and again. No settings have been made yet.
Next, I decided to try installing Windows 10 on my computer to test it. The installation freezes completely after the first step.
As a result, the ideas ran out, the computer was turned off and put away. Maybe I'll throw it away later.
Thank you all so much for your help!