Davidb

That can't be the fault of the inverters; it will be to do with the way that the battery modules and/or the inverters are wired.
Perhaps you could post (a) photo(s) of the battery and inverter wiring, please? Hopefully there is a busbar, and some attempt to keep the battery and inverter wire lengths close to each other. It's probably more important to get the battery module wiring right than the inverters, unless you need to repeatedly run the inverters near their rated limit.
The other thing is that perhaps the battery modules were connected together without bringing them to the same state of charge. If so, it will take weeks or months to equalise the charge between the modules. You might be able to balance them yourself by turning off whichever one has the highest state of charge until the others catch up. But it might be necessary to physically disconnect one of the wires to that module, while still making a high  current connection to the others around it. This may take a little ingenuity, or some help from someone knowledgeable.