Vim: how do I clear all marks?

Solution 1:

:delm[arks]!        Delete all marks for the current buffer, but not marks
            A-Z or 0-9.
            {not in Vi}

• 'A - 'Z uppercase marks, also called file marks, valid between files
• '0 - '9 numbered marks set from .viminfo file.

To delete them:

:delmarks A-Z0-9

Note: ~/.viminfo contains histories and marks, if you don't want them any more, you can delete this file. Vim will recreate it next time.

So, you can do this to clear all marks:

:delm! | delm A-Z0-9

Solution 2:

Vim stores this type of information in ~/.viminfo. This file holds much more information than just marks by default. The exact information stored can be controlled by the 'viminfo' option.

See :help 'viminfo' for more information about disabling specific features.

You may be able to "fix" your issue by removing this file and having vim recreate it when you start it again. Be aware that you'll lose the extra information stored there but I believe your marks should all be cleared.