Something is currently broken in modpost.
I'm guessing it is down to the recent patch that moved the
namespace back to the end of the line.
I'm building 2 'out of tree' modules that have a symbol dependency.
When I build the 2nd module I get ERROR "symbol" undefined message.
If I flip the order of the fields in Module.symver to the older order
and link with modpost from 5.4.0-rc7 (which I happen to have lurking)
it all works fine.
Note that I'm using a named namespace, not the default one
that is the full path of the module.
I'll dig in a little further.