Hitting a Brick wall
Of my GMing failures (and there have been plenty), the most common causes have been communication and engagement.
Engagement is the quicker of the two to describe. In short, if you can't "be in" the game, that will often manifest itself in little things that will damage your game. If you feel uncertain about the rules, you might be unsteady in your execution. If you have an RL issue dragging at you, your posts might not be what they should. Whatever it is, something keeps you from really driving your game, and that often trickles down to players.
Communication is a broader topic, but is the very lifeblood of RPOL games. Communication starts before the first RTJ is sent. If your players aren't clear on exactly what they are signing up for, you are going to lose some of them. If you are using lots of system tweaks, it is the same way. Once the game starts, clear communication can make up for game disruptions and manage e expectations before problems arise.