What causes uneven evaporation of lead acid battery electrolyte?
When cells get oxidized from under voltage for long periods (lead sulphate) they develop higher ESR.  The 14.2V is most commonly used on flooded cells to lightly   agitate the plates with extra current to break down this oxide so it settles below the plates.
The weakest cell will accelerate its overcharging when there is 14.5V and instead of 14.2/6 you start to generate more heat from I^2ESR losses in one cell more than the others with lower voltage and start to boil off the acid. How well matched each cell capacity in kFarads also affects the voltage rise in each cell, so the weakest cell again overcharges and boils off more electrolyte.
The best way is to limit the voltage to 14.2 abs. Max and measure specific gravity , s.g. with a glass float and rubber hose with a sample for each cell. Quality of a battery with series cells is not only the high capacitance (Ah)  and low ESR (CCA) but more importantly , how well matched they are.
Pulse discharging is an effective tool which can also desulphanate batteries when the  battery is being charged &gt;13.2V.  If the sulphated condition is short term in months and ambient temperature is not too high &gt;40’C the sooner this is done, the better your chances of recovery.  Otherwise name brands mean nothing while perfectly matched high s.g. Means everything to a open flooded lead acid battery within 0.1%. 10% difference is poor.