Your panels would be better wired in series, they really are at the lower acceptable voltage range and so!e deterioration may have occurred dropping them too low. Are these flexible panels, lower quality low price flexible panels on boats often do not have a long life.
If the battery was limiting charging it would be at 14.4V or whatever your absorption voltage is.
You may have a failing panel(s) or a poor connector, loose wiring to a device, poor breaker etc causing voltage drop but this normally reduces the panel voltage to the battery voltage.
Panel checking guidance below