As you have 4 batteries in series, have you ever checked that they are all balanced, i.e. when charged that they all charge to the full voltage and in use stay at the same voltage. When the voltage dipped were all batteries dropping in voltage or just one of them. Do you only take off 24V load, or do you have any 12V load taken from the mid point. Taking 12V off is not a good idea as the batteries get out of balance.
How do you charge them and are you sure you are getting them full. For Rolls batteries to fail after 2 years of easy use suggests undercharging to me. Are you getting them up to 28.8V and less that 2A charge current regularly. Are you stopping charging when the shunt states 100% because it can say that prematurely if you have not set it right and you use solar charging. What absorption voltage do you use and what charged voltage do you have on your shunt.
See my FAQ in the DIY section as this may be the issue.
https://community.victronenergy.com/t/shunt-battery-monitor-jumping-to-100-or-reporting-a-high-soc-when-the-volts-are-low-and-or-the-bms-has-disconnected/88
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