What @mcalista said. If your left / right balance is 55/45, then bePRO S will read 110, and the Neo will read 100. That’s a 10% difference, or 20 watts if you’re pedalling at 200 w. My complaint about the bePRO was that it broke down after 3 years and 3 months, but accuracy was never a problem (according to DC Rainmaker)
Also, there could of course be a calibration problem with either the Neo or the bePRO pedal. Might help if you uninstall bePRO, reinstall it, do a dynamic calibration (then static of course) and see if there are any changes vs. the Neo.