ESP8266 run on strange speed after power on

The controller has worked steadily for over two years. Recently, data in Google cloud iot stopped coming in. After connected to UART, I have found that the controller was sending debug information at an incorrect speed - 74800. This is not a short log on boot, but a full log of my firmware. By repeating the on / off cycle several times, it was possible to achieve the output of the log at the correct speed.
The controller was successfully flashed, but after turning on / off it showed the same effect again .
My goal is to achieve stable controller work.
Does anybody have any ideas what I can do to make the controller work steadily?

My first impression is that either your hard goes crazy or your firmware goes crazy and writes where it shouldn’t.
However, hw issues would probably also affect other parts of your system. Flash other device to check for hardware, if it is a firmware problem then check for runaway pointers as usual. Do you have C code in there ?. Since “it’s been working”, one would discard firmware, but sometimes bugs lurk until something triggers them.
Can you be more specific about the GCP stuff ? Does your WiFi work ? Do you actually connect ?