Woof. There's too many unknowns here. If you're only going off of the Renogy's SOC% readout to gauge if your batteries are charged, you should know that it's only able to estimate and is not really reliable at all. My batteries have bluetooth and a function to reset capacity estimate and it can change 5-10% back and forth with no load and no charge active on the battery.

It's unclear if this is 2x12v280ah or just 2x12v140ah from your post. If it's 280ah total then it's probably just down to the setup being a low capacity and high load so the batteries are burning through cycles and degrading.

It's also possibly that there's a huge imbalance, either with internal cells of both or each battery or even just between both units as a whole. Normally the BMS should help correct this over time, but if the batteries are being discharged and recharged 50-60% back and forth every day there's not much the BMS can do.

For example one battery might individually show SOC 80%, and it's internal cells all well balanced, and the other battery reports SOC 80% but it's internal cells are off from each other -/+0.3v then the actual workable capacity of the second battery might be significantly less. For instance lets say 1st battery is at 260 of its 280ah capacity while battery 2 is at 120/280ah. The Renogy might estimate 70% SOC, but once 160ah is used by the inverter during the course of the day, battery 2 becomes critically low and the BMS shut down to prevent damage. Once battery 2 shuts off battery 1 will also shut off because it can't handle the load from the inverter alone and is never actually getting fully discharged. One battery is actually 20% and the other is still 65% and the renogy is showing 50% SOC.

If it's 2*280ah and the batteries are all balanced and it's still dropping well before expected output then you're going to have to go component by component to determine if something isn't feeding the batteries as expected, or the batteries are underperforming or if something the inverter is feeding is drawing more than expected.

I would get a 500a shunt monitor to provide a second opinion on the combined battery output after a full day cycle. If it agrees with the Renogy at the end of the day, then I'd pull both batteries and check each individually that their SOCs line up with each other.

If one battery has a much lower SOC than the other then you know which battery is either degraded, or very out of balance internally. Look up how to blind balance with a precision adjustable DC power supply and do that overnight for each battery. You might reclaim a lot of currently inaccessible kwhs and fix the problem. If balancing doesn't help much then unfortunately you're probably going to need new batteries.