I concur with Aggie.
With RC paper it probably is not enough agitation and getting the print fully emerged. Remember, if you develop RC for 1 minute and part of the print does not begin devloping for 6 seconds, you have a 10% reduction is development. One easy way to test is to leave a print in for 2 or three minutes and see if the spots develop out.
My procedure (with fiber based) is to start the paper face down, with the tray lifted so when I place the sheet in the tray and as I set the tray down a wave of developer quickly covers the print. Then I rock the tray from a couple of different corners and then flip the print over after about 30 seconds, and continue constant agitation for the prescribed time for that paper and developer combo.