Bitcoin core has been stuck syncing to the network This keeps repeating in the log file:

2020-04-16T23:59:53Z ERROR: AcceptBlockHeader: block 0000000000000000000fb8b3828b04c17205ffcdedddc8be1d400d132d336460 is marked invalid
The only answer I could come up with myself was to "unprune" the blockchain to force it to redownload. I then reactivated the "prune" feature and restarted the blockchain download. I think the block was corrupted - we'll see.