Undefined anything always means that a part of the javascript tried to use an object that has not yet been defined.
And that can have only very few causes:
1) a plugin accessing data that is not defined or not configured
2) compatibility issues between two files (either core or plugin files)
3) misconfigured plugin
4) loading an incompatible save
5) damaged javascript code
If it happens before the title and when all plugins are disabled, it is an incompatible or damaged core file - please update your project's core files with files from a new, up-to-date project (instructions for this are in any update topic of MV, it's the same procedure for updating projects to a new version).