The snapshot of your mqtt-in nodes in that Adafruit forum shows 27 nodes, all subscribing to kd0ycl/f/something.
You can certainly replace all of these with a single subscription to kd0ycl/f/+ or kd0ycl/f/#, reducing your subscribe message volume by 95%.
This is surely the way to go, no need for the more complex dynamic subscription (which anyway you have found the problem with)
If you want to avoid the massive switch node on your flow tab you could have the mqtt-in and switch on it's own tab, using link nodes to pass messages to the tab[s] where you process them.
