Shoot, I transferred 400k GPUC and they're not showing on the receiver wallet

If they went transfered on the wrong blockchain, does this means that my coins are lost?

No, not lost.
Could be due to several different issues that plague a lot of wallets on a lot of coins.
Re-downloading the block-chain on both clients while running the wallet with the re-scan option in the shortcut you use to launch them should solve almost any issue, especially if afterwards you wait approx. 30 minutes for any thing missed in blockchain to be re-broadcast and confirmed. Any questions just ask here.
waltsmith