Quick update: What we ended up doing was restoring it at the brokerage address and moving it back to the original private address, which when then hid. The client has no other profiles in the Montreal area.
How would you suggest handling multiple profiles tied to a single address? Like Realtors tied to a brokerage address?
I am aware of hiding home address as option vs using brokerage address. Negative impacts to hiding address?
There is no foolproof solution to avoiding the Google filter system for GBPs that share an address. I've seen a little more leniency in how many brokers can show (e.g. up to 4 out of 14, which is a much higher ratio than I would've expected two years ago!), but our trick is basically
don't have two clients with the same address in the same vertical, period 
otherwise you're setting yourself for endless pain as they will wrestle for the same keyword (and that is not even accounting for possible competition.).
Hiding the address will avoid filtering from other profiles with displayed addresses,
but if you have more than one SAB with the same address, you're back to square one, and you can't hope for the amount of profiles at the address to increase your chances of displaying both anymore!
We rarely have that issue with real estate agents (we usually end up with people with different offices), but we have run into cases where two denturists or massage therapists were sold that were in the same building, and that was no fun for anyone involved.
In terms of rankings, we don't see much difference from a hidden address anymore, but you do sometimes have to contend with some weird behind-the-scenes tomfoolery on top of the usual map display bugs. You see, the address is no longer visible to you, but G
oogle can still change it. Specifically, we recently had a duplicate merged with our SAB, and the duplicate's address "took over", forcefully displacing the rankings for our client several towns over from her actual target area. That was one weird case to sherlock holmes our way out of, for sure!