Error on production - base of object #?

I am trying to put a site up in production and as soon I hit F5 / refresh I get the error

Cannot assign to read only property ‘base’ of object ‘#’

Console shows nothing to provide any hint or clue.
I have no issues running the site in dev localy, but when I run build then start on the server as stated, runs fine until I hit F5.

No idea what ‘base’ is. Is it me? Is it Vue? No clue what it is or where its comiing from.

Any ideas / suggestions / assistance would be greatly appreciated.

Thanks,

Dave