RIGOL Oscilloscope timescale "bug"
Your Keysight scope is sampling at 1 MSa/s. I can't quite make out the Rigol's sample rate, but it looks like 5 MSa/s. That might account for some of the difference. Regardless, neither of those sample rates is high enough to correctly show a 20 MHz signal. You're seeing garbage on both scopes; it's just different kinds of garbage.