Could you please check if you have multiple pathdef.m files in your path?

>> which -all pathdef.m
The 'pathdef.m' that is currently used must be the one pertaining to the release of MATLAB you are using currently. If an older 'pathdef.m' exists, it will shadow the new one and does not add the directory to the path, which results in the error.
Renaming the old 'pathdef.m', if you have one, should fix the error.

*This seems like it might be a common issue with Matlab2017a