i finally got synced today, took 2-3 days, it froze once and i had the same problem with sync returned unknown block, i saved and restarted aswell and it fixed the problem...
edit: running on ubuntu
Monero Node Syncing Taking Forever?
penorzilla posted this 8 years ago
I have tried on both SSD and HDD but when syncing my node with the blockchain around 80,000th block it starts to run very slowly and I'm getting a lot of "sync returned unknown top block" then followed with "SYNCHRONIZATION STARTED" and repeat... with about 15 seconds inbetween outputs. Responds to save commands immediately so the terminal isn't being locked up.
This happened on both Windows 10 and Ubuntu Server.
Is this just because theres a lot of stuff going on in Monero right now?
Type "status" in the daemon, and note the current block height you're at
Then, after a minute, type "status" again. If the current block height is the same, then you're somehow trying to sync to a wrong chain or something. Or your blockchain became corrupt for some reason, in which case try exiting daemon, remove data.mdb (the blockchain), and start again.
I saved the blockchain and restarted the node and it appeared to clear it up.
It appears to get stuck after X hours of running multiple times. Saving and restarting it fixed every time.