New info: after a few days of debugging, here's what I've learned:
- I installed a new NIC - same make/model as previous: Intel Gigabit CT Desktop Adapter (PCI-E, 1x channel). No change in behavior - so I can at least rule this out this HW as a failure point. Curious that this NIC also fails the loopback test - but perhaps I'm not running that test correctly (i.e. I leave it connected to the router).
- Downloading large files (>5MB) works fine with FTP - the problem appears to be with HTTP downloads only
- Behavior is the same with IE (v11) and Firefox (40.0.3) browsers - FTP files download with no problem - HTTP downloads are either interrupted, or when they download they are corrupt (invalid signature and/or CRC error)
- Ran a memory test (Windows Memory Diagnostic) on the desktop - no errors
Hoping these clues leads someone to a possible cause (and fix!).
Thx