iCloud drive not syncing on my iMac

I am having problems accessing documents from iCloud on my iMac. I access iCloud drive in Finder on both my Macbook and iMac. On my Macbook, my files seem to sync seamlessly and quickly with iCloud drive (checking with what's showing on iCloud via my web browser), and I can access all of them. However, on my iMac... most of the files have not synced at all and I get the "available for download" cloud symbol next to about 75% of my documents. I can't open any of these documents on my iMac that have this cloud symbol next to them. I've been searching for some way to sync these on my iMac so that I can access them, but cant' find any info on this. Help!