Put some lava for guardians to fall out, but they try to swim over the lava. this is not happening in 1.13.2. This can happen with other mobs as well.
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is duplicated by 8
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Also occurs in 1.14.2
The guardians never fall thru the lava killing chamber of the farm, but instead most of them end up dying in the lava (only 1 block tall).
Apparently their AI when it falls into the lava, from the water, they think (Some) that they are still in water and remain floating, possibly due to their movements and their better AI than that of squid
Can confirm that guardians try to swim in lava.