It seems to be making progress in the Web UI and it shows in the bottom right, "70% warp restore, Homestead, 1/26/50 peers". After about 70%, it seems to encounter an error and restarts the warp restore. In console, parity prints out the following and then starts "syncing snapshots" from 0/313 again. It always gets to about 160 and then restarts.
2017-06-18 17:59:45 UTC Syncing snapshot 160/313 #59186 3/26/50 peers 156 MiB db 3 MiB chain 0 bytes queue 9 MiB sync RPC: 0 conn, 0 req/s, 195 µs
2017-06-18 17:59:50 UTC Encountered error during block restoration: Block error (Block has invalid PoW: Value 0 out of bounds. Min=735388763471630)
Any help would be much appreciated!