"Unlike a normal grid-tied inverter, the Storeredge inverter has the capability to throttle it's output."
Not sure where you got that idea. All grid-tied inverters 'throttle their output' to match the frequency and voltage of the grid, the same way off-grid inverters adjust their output to whatever load is applied.
Not sure what is going on with your system unless you are exceeding the capacity of the inverter in your Powerwall. Or it could be having trouble with the combined inductive/resistive load from your hot tub. Jeez, I ran a hot tub off of my two old Trace 4024 inverters for a couple of years. What's the amp rating for your hot tub?
The beauty of an off-grid hybrid system is that the PV and the controllers run essentially independently from the inverter. The controllers will continue to charge the batteries (up to their set charge parameters) whether or not the inverter is feeding the grid or drawing from the battery. The problem I have with grid-tied inverters where one unit combines charge controlling and inverter => dreaded single point of failure. I could lose one or more of my charge controllers and one or two inverters and still keep things running until repairs can be made. Goes to redundancy and resilience.
If I was a gridweenie, the inverters could charge the battery from the grid if battery voltage drops too low, or (not being a gridweenie) either the controllers or the inverters can start the generator (provide power AND charge the batteries). If I added a hybrid inverter/charger like an Outback Radian, (and was a gridweenie) I could sell power to the grid. Indeed, I could set it to ONLY sell and never draw from the grid. I can set the system to dump surplus power to hot water, or turn off non-critical loads when battery voltage drops below a set-point.
Love the versatility of my system.
Not trying to instill buyer's remorse or criticize your system. Enjoying your posts and am sure you'll figure things out with time. It took me a few years to grok these things.
What is the rated output voltage of your PV string(s).?