You’ve gotten very good advice so far. It’s not likely to have anything to do with battery versus hardwire, but sometimes it’s the specific location, down to within three or 4 inches, that’s a problem.
So far you’ve tried swapping out one wired zwave switch for another, I understand that. As a field tech, my next step would be to take the switch out of the wall all together and move one of the battery operated devices which is working in the garage to the location where the switch is. See if it fails in that location. If it does, that tells you there’s a micro location issue, something right in that wall or on that wall or as was suggested maybe a frequency interference from something like a baby monitor or old cordless phone that just happens to be hitting that spot.
There’s no harm in trying a zigbee switch or WiFi Switch there instead of a Z wave switch if you think the battery operated devices aren’t using that switch as a repeater anyway.
Sometimes it just takes a lot of trial and error to find out what the issue is in a particular spot in a particular building. If you have network tools, it’s way easier, but smartthings doesn’t give us any. 
As it happens, if you’re one of those people who will just go crazy until you figure out exactly what’s happening, there is an installer tool set that’s on sale right now for $189, but that’s a lot of money to spend just to satisfy your curiosity.
Without that kind of tool, you just have to keep trying different combinations of devices and locations until you find something that works for you.
If I were in your situation and I felt that I really didn’t need a Z wave repeater in that location I would probably shift to a Wi-Fi switch just because they have great range and they are likely to work the first time this particular kind of set up. But obviously that’s up to you.