I tested this unit (Multiplus 24/3000/70-50) with no AC loads connected (I removed the wires). When turning it on, the inverter LED comes on for a second or so, then switches to the red Overload LED. It's solid, not blinking.
Firmware is now 2712481. I purchased the unit July 5, 2018 through Amazon and installed it myself. It's also connected to a Venus GX.
It seems like the answer here is to contact a local resource for repair/diagnosis?