I would read through this thread:
https://community.rachio.com/t/flow-meter-not-working-rachio-please-help/17163
The WFM can only resolve flow rates up to 25gpm. It does know that there is an overflow condition and Rachio should report it as such. If not, it may show 0gpm. Obviously, 60gpm is way beyond its range and way beyond the specified acceptable range of 1" PVC pipe. (Not to say that people don’t try to use it this high)
That explains the flowmeter readings, but I can’t explain how you have enough pressure to get astronomical flow rates like that. You must have an incredible shower.