I mean it's got to be something to due with either BRGC or OpenOS. When I shut down BRGC and manually change rod insertion on the reactor it can provide steam to all the turbines fine. It gets low on water due to the storage limit as you said, but at never runs out or fails to pump out enough steam properly.
For now what I've been doing when I want to leave it in "charge" mode (my goal is to reach 1% full on my energy core), is to turn the reactor "off" in BRGC so it doesn't mess with it, then manually turn the reactor on and adjust the rods to output 32B/t. This is hardly ideal since