Republic has always recommended both mobile data and roaming data be turned on in Android settings. The reason behind said recommendation has everything to do with the way Republic’s unique and patented blended WiFi/cell service works and nothing to do with any intent to expose one to insecure cell towers. May we know what was updated? The only thing Republic updates on our phones is its app. If it was Android itself that was updated, that was the manufacturer’s doing.
If it is the Republic app, i’m not aware of anything in a recent update requiring roaming data to be turned on though as mentioned that is and always has been Republic’s recommendation. Roaming also has nothing to do with whether one is at home or not. Roaming refers to a use of cellular towers other than one of Republic’s network partners when those partners lack native coverage in a given area.
It isn’t even a certainty your Moto Z play uses Sprint towers. While true that older legacy Republic phones were provisioned for cellular coverage with Sprint, newer Republic compatible phones like your Moto Z play might be provisioned for cellular coverage with either T-Mobile or Sprint. Of course, T-Mobile now owns Sprint but the networks remain separate. If you’d like to verify which of Republic’s partners your Moto Z play is provisioned with, please see here: How to Tell If a Phone Is Active on GSM or CDMA – Republic Help.
Finally, and out of curiosity, what would make Sprint towers more secure than say T-Mobile or for that matter AT&T or Verizon? These days even for native coverage the network operators generally lease tower space rather than own the towers themselves.