Agreed. That why I thought trying the switchover and status from SQL might either either shake out the clue we need or allow the switchover from SQL. In the latter case I think that this means a broker has a bug. I search the Oracle support notes looking for exactly that, but came up empty.
The reason I thought try with no Broker is Broker will add parameters to your INIT file. So if we created a Pfile from spfile and checked it for those and then removed and created a new spfile. The the SQL
switchover attempt could be tried.