This is my first experience to have an io-error status on my Proxmox VE. Based on several explanation on Proxmox forum this io-error is mostly correlated with the local disk. For example the disk is full so it cannot handle more data or cache. Another reason such as the disk is dying will also display io-error status.
In my case, my disk is full and there is no other workaround that I can do to solve the problem. I need to free up some space to my Proxmox disk. And now it working again. So, if you have io-error on your VM status, make sure the disk is not full.