I got the 5x boost on my main to see how it went, and achieved the first reward from hitting 25k RP (I had 26-some K last I looked). Then, I did some stuff and went back to PE, and noticed my reward bar dropped back down to 10.5k, no longer at the first reward marker.
I put in a bug report and contacted customer service (who apparently couldn't help me?), but I'm not sure what else to do. Is this a thing that's happened to anyone else? Is there something else I can do?