I had a similar problem today. I’m on Windows 10 machine, running Daedalus 2.1.0 which had a fully synced chain as of yesterday. I have 1GB fiber network, and my machine was only running Daedalus.
When I started the machine this morning, the site says 99% synced. It took 5 hours to finish the chain averaging 0.01% about every 8-9 mins.
To trouble shoot, I’d stopped my firewall, and virus protections. I restarted the computer and Daedalus. On restart the counter was slightly lower than at shutdown.
Watching network traffic, it looked like the software downloaded the entire chain again, although looking at the individual chain chunks in the …/chain/immutable folder, all of the datestamps were from the initial sync a couple of days ago.
Looks to be a problem here worth investigating.
(may be related or not, but my spending password also stopped working today. I used a copy and paste on that and it worked yesterday when Daedalus synced, so it wouldn’t seem to be a user memory problem. I had to delete the entire wallet and restore to get it to work.)