BMS Low Volt Cutoff in a multi-BMS setup

Just built my first large battery pack (~600Wh) to power a small Inverter and some DC appliances when I go camping. I designed the system with 3 individual batteries (made up of 49 cells in a 7s7p configuration). Each battery has two Dewin 24V 20A 7S Lithium Li-ion 18650 Battery, BMS Protection Board with Balancing connected in parallel protecting the pack. I used salvaged 18650 cells ranging in capacity from 1,400 to ~1,150mAh.

Just trying to make sense of the shutdown characteristics here --> when the entire system hits something like ~23v it all shuts down. I am assuming this is happening when the lowest capacity of the 3 packs (built with the poorest cells at ~1,200mAh) hits its low voltage cut-off, it causes a surge and corresponding voltage sag across the good packs. I can reconnect the other 2 packs and continue powering the same load for another 30 minutes or so, but without the manual off/on process, the entire system stays off.

Is there a way to stop this from happening (e.g., introducing a high capacity capacitor / how would I size that properly)? Have I diagnosed it properly? Am I a moron for using old cells? Thoughts?