Root cause
The root cause of this issue as the user's viminfo file gets corrupted somehow and certain characters are not interpreted so every time you try to open the original file, it throws out "Illegal starting char in line"
Solution
You can delete the user's viminfo file from the user's home directory which exists in current login user
.viminfo file is hidden file as started with .(dot)
Which file contains information about the history of all the vim editor records such as files edited and the arguments you used inside the editor etc.,
There is no interruption will happen to affect any of your existing work due to removing the file as .viminfo. Its also the better way to erase your cache history but it does not affect any of your work done.