mmc0: error -110 whilst initialising SD card [closed]

Basically this error arises only when the SDcard got damaged. But as you mentioned its working, Please try the following steps and share your feedback.

• Please check the output of dmesg or lsusb to check whether it detects the SD card.
• Open the "Disk Utility" application and check whether your SD card is listed. If its listed, just click it -> Unmount Volume -> Format the Volume with suitable filesystem.
• Also, try mounting the SD card on Windows and check whether it is working or not.

Also, you can downgrade your kernel by installing the old kernel / latest stable kernel version with sudo apt-get update && sudo apt-get dist-upgrade && sudo apt-get autoremove.

wget the latest stable kernal from Kernel Website and install it with sudo dpkg -i *.deb && sudo update-grub2

Please select the proper kernel while booting and check whether your SD card mounts well!