Do you have wifi that have multiple streams from same ssid ? I have seen this issue from apple airport extreme since it generate multiple streams with extended network. BTW other extended network devices do the same..
Issue is you may have 5ghz and 2 ghz streams generating from your wifi router and the device you may (iPhone) use may be 5 ghz and for some reason open garage iOS app only work with if you are in the same stream as your principal (iPhone or laptop etc..).. Very poor way to design a app..