Albert Barnes Commentary Jeremiah 52:20

"The two pillars, the one sea, and the twelve brazen bulls that were under the bases, which king Solomon had made for the house of Jehovah-the brass of all these vessels was without weight." — Jeremiah 52:20 (ASV)

twelve brasen bulls that were under - Omitted in 2 Kings and in Jeremiah 27:19. This was probably correct, because the statement here about them being under the bases is a mistake. The bases were under the ten lavers. The Septuagint makes sense by translating it: “the twelve brasen bulls under the sea.”