I have the same problem. I downloaded 5.5 wallet and bootstrap file. Wallet had right updated the blocks of booststrap but is not able to finish blokchain upgrade. In real time i have from 4 to 6 active connections, and wallet is downloading new blocks, but I have a permanent gap from wallet and blokchain of 700/800 blokcs. In this minute, while I'm writing, wallet say " Upgraded" 1102858 blokcs processed and dont say out of sync. But the blockain Explorer shows block 1103638 as the last.
Can sameone help me in this? Many thanks in advance