Inverter Error/Fault 09 -- Cause?

In recent months I purchased a 5KVA 48V (Suoer) hybrid inverter. Sometimes when I have had to shut it down to do some maintenance and then re-connected the (LiFePO4) 48V battery to the inverter, I get a 09 Fault/error when I turn the inverter on, and it will not power up. (I now understand that this inverter uses the same board that many other makes of inverters use--confirmed by the fact that the user's manual for this model is virtually identical to a 5KVA model made by Voltronic (Axpert), etc.--so that's one reason I'm hoping that perhaps someone reading this post might have also experienced this problem.)

The first couple times I got the error, I assumed I would have to get it repaired, but each time I've gotten that error, after I let the system set for a while (usually overnight), I try powering it on again, and it works fine. Do you have any experience with a hybrid inverter of this type? Anyone have a suggestion what might be causing this intermittent error and/or how to avoid it? (I wondered whether it could be the large surge that caused a healthy spark when I connected the positive lead, but I doubt it.)

On other forums, some have observed this error when they had fried MosFETS, etc., but since the system has usually worked the next day, I tend to doubt that it's caused by blown part(s).

Appreciate any suggestions.