@Michael-Lynch
Sorry for such delay - I was fighting against this problem. Your suggestion was hopeful but it didn't help me. I hope your suggestion will help other people who will face this kind of problem.
I've suddenly noticed that I can see correct symbols of bootloader output on the baud rate 120000 (instead of expected 115200). However, the baud rate of the kernel has to remain 115200. Firstly I thought that it is a manufacturing defect but I've noticed such a thing on the few devices. Also, I've entered into the console mode of the bootloader: the expected baud rate is 115200 (variable baudrate=115200).
@Omega-Squad , @administrators @cas
I'm using Omega2+ devices. What is the reason for this bug? I'm a little bit confused about how to deal with this problem. I hope for your understanding.

@Michael-Lynch
Thank you very much! I'll try your suggestion and respond if it works.

I'm using the required driver CH340 on my Windows PC

Hi.
I've got the following problem. I'm trying to flash the firmware from my USB drive. So I press the "Reset" button and see that LED starts blinking. My COM port is opened via Putty. However, I see strange characters although some characters seem to be correct. I'm trying to press "1" or "2" option but without any success.

When the bootloader is loaded (after 40 seconds) it starts to uncompress image. Then everything is OK.

What is wrong with the UART and bootloader? There is some noise. I've tried to connect UART pins directly with my UART-USB adapter but it didn't help. Also, I'd like to mention that I didn't change the bootloader.