Almost always after updating coreelec I have this info:
Could not mount LABEL = COREELEC
But usually it helps to connect a pendrive / sdcard to pc and the label somehow returns (sometimes pc does not see either the card or the pendrive after removing it from the box and connecting it to the pc, you have to do it several times until the files appear in the file manager) < visible>![do not format]< /visible>