After upgrading to Coreelec 19.2-Matrix_RC2 p281 1G RAM is not booting

Then I do not know what do do next.

The only way would be to open your device and search for the UART header and make a UART log as you can not connect by SSH.
The easier method will be the SDIO debug board but I think as the device already “old” you invest your money into a newer device with a newer SoC (S905X2 or the more preferred one S905X3).

Look here: