This is fairly common on Epiphone Tune-o-Matic bridges. String tension is unseating the ferrules into which the height adjustment bolts thread. Loosen the strings to get the tension off the tailpiece, remove the bolts and tailpiece, apply some non-permanent adhesive to the bolt ferrules and tap them lightly into place. Once the glue has set, redo your set-up. If the tailpiece remains in place but the bridge still puills forward, see if you cannot effect a similar fix with the bridge.
All this being said, I second @RubioClaves suggestion above. Ditch all that heavy metal and get a short trapeze tailpiece (like for a violin bass) and a wooden floating bridge. Your bass will be lighter and look better.