After getting nectar, bees can usually grow 10 plants. But in the case of cave vines, the target block is never updated, causing a null check to pass and skip the increment of the crop counter. I have attached a screenshot of the decompiled function (I hope this is ok! yarn mappings). In the highlighted area, the lv4 variable isn't updated, which causes the "continue" statement to execute, thus skipping the addCropCounter() method.

The effect is infinite growth boost of cave vines as can be seen in this video https://youtu.be/9abyzXZ0p9I?t=787