Are you getting a warning about "High mobile data use" or looking at your device's data stats and seeing that the Circle app is causing a lot of traffic? We can explain!
Your operating system is likely counting all of the device's internet traffic towards the Circle app.
Basically, to understand what's happening here we first need to understand how a VPN works. The acronym stands for Virtual Private Network, and it can be used to tunnel a device back to another network. In Circle's case, that VPN is local but all traffic that goes through it is attributed to the Circle app.
This means that every internet-based request on the phone is technically utilizing the Circle app VPN to connect. This can cause your phone's operating system to incorrectly report that Circle is using more data than it actually is.