The RBW can only be achieved by manually setting the sample rate in the menu.
If you leave the settings on Auto, you get a different value - which RBW is the "right" one for a 50Mhz signal and 1Mhz span (50k, 10k)?
For example, if I leave the SDS3034X HD as it is, I have approx. 700Hz RBW, but also no "problems" with the signal display.