Continue tracking on another device
One phone records a track. Another device of yours can take it over, and the first one stops at once.
A GPS track records on one device: the phone that started it. The training page on your other device says You are tracking on another device, and under the title the training shows who is tracking.
To take over, tap Continue on this device. The app asks first. From then on this device records, and the device the track left closes its recorder immediately. Points the first device still had are sent along; nothing is lost.
The device that records shows Back to tracking instead of Start tracking on the training.