This won't help you - but I have the Watch 6 too and it did work until sometime quite recently - probably the last update - and now it doesn't give you the option to set a place. If you set the reminder by voice and say something like 'remind me to put the bins out when I arrive at home', it sets the reminder, but does not add the location (it used to).
So it looks like Samsung have broken it! This might be the final nail in the coffin for me to jump ship to iOS as there are just too many things that are half-baked with Samsung & Google.
