I left CLAM alone for about 80 days, then restarted it a few days ago - and it's still trying to sync...

The debug log is full of "already have block" and "ORPHAN BLOCK 751" entries.

2017-05-08 10:22:14 SetBestChain: new best=e14bb9bc8557e99af05120468920505f7c1208fdb321a9124e41234659fd420a  height=1486871  trust=466372186589834826465  blocktrust=338273748876064  date=04/28/17 01:14:40
2017-05-08 10:22:26 ERROR: ProcessBlock() : already have block 1486871 e14bb9bc8557e99af05120468920505f7c1208fdb321a9124e41234659fd420a
2017-05-08 10:22:26 ERROR: ProcessBlock() : already have block 1486871 e14bb9bc8557e99af05120468920505f7c1208fdb321a9124e41234659fd420a
2017-05-08 10:22:30 ERROR: ProcessBlock() : already have block 1486871 e14bb9bc8557e99af05120468920505f7c1208fdb321a9124e41234659fd420a

Here's a random but typical example. The same block was received four times over a period of 16 seconds.

Why are peers sending blocks multiple times, and seemingly (due to all the orphan blocks) out of order?

It's taken 3 or 4 days just to advance the blockchain by a couple of months. Any further work on fixing this?