I am experiencing the same issue. Pamac started downloading normally (I used the TTY) and then seemed to stop - at least I got the output: “terminated” even though there were only about half of the packages downloaded. However, I noticed that pamac was still running in the background so I waited.
After several minutes my laptop stopped making noise so I ran “pamac checkupdates” and it gave me the output, that my system was up to date.
I will try rebooting now and see if the update worked out okay…fingers crossed!
Edit: I rebooted and everything seems to work fine 
Just as an info: I DID run sudo pacman -Sy libpamac before I started the update, but experienced the issue nevertheless…