When you empty the collector bag, or what ever it uses, there are still leaves packed up inside the chute that the wind force can't push into a full bagger. Then if you don't clear out those packed leaves, the next time you start the mower it won't have enough power to push out the leaves in the clogged chute--therefor giving the problem you have now! Do not try to clear out that chute with the mower running! Or, the deck in gear! You could get yer fingers chopped off quickly!

I clear it all out before I fire it up again. It's an RPM issue; it's like the throttle is set on super turtle even though I have it on the rabbit.

You probably need to check a few things - there are a number of conditions that could cause this. We'll start with the simplest; next time it does this, take a stick like a dowel rod, ruler, etc. and push the air vane over from the LH side of the mower. The engine should race. If the vane seems 'sticky', there's your problem. There is no hard linkage between the throttle lever and the throttle plate in the carb. The cable moves a slider on a wire bracket back and forth on top of the air box, to which a tiny spring is attached that pre-loads the air vane/throttle plate. The knurled collar at the base of the vane is the adjustment for the governor spring. The governor spring can break or need adjustment, and the wire bracket can get partially detached from it's mount. Also, the air vane can stick in the carburetor.
Now do a quick check - remove the air cleaner element and look in the carb - with engine off, the throttle plate is normally in the wide-open position. Work the air vane and release to see if it freely snaps back to the wide-open position. It could be as simple as a small stick or other obstruction binding the governor.
If you can get the engine to race by manipulating the air vane, many other problems are eliminated. If it works, you'll then need to see what is sticking. Drain the fuel tank and take the tank shroud off and slide it up the starter cord so you can see the steel air shroud and carb. Work the throttle to see if the slider moves and check the wire bracket to see if it is attached. See that the governor spring is attached to the slider and air vane. The governor system might just be dirty, so clean accordingly.
If you think the vane shaft is binding in the carb, which is what it sounds like to me, just working it a few times might free it. When I was using 2-cycle LBs, I learned to add about 2 oz/gal of Marvel Mystery Oil to the mix in addition to the regular 2-cycle oil which is really good for 2-cycles in every respect. This may well dissolve gum/carbon around the vane shaft over time and keep it running right. Let us know what you find.
BTW, if it runs normally from a cold start, chances are you do not need to adjust the governor collar. If the engine always runs slow, you adjust that by giving it 2 to 4 clicks clockwise to pick up 50-100 RPM.