Nextcloud - syncing super slowly! / syncing is stuck?

i’m not sure what’s gone wrong, but i am trying to migrate the contents of a shared file server from dropbox to a more securely hosted cloud. the nextcloud clients are on all machines and up and running. however, since migrating the contents to the cloud, the client seems to be stuck. it oscillates from 12 to 15 hours remaining in the syncing. something must to be wrong with the configuration. i don’t know. it worked fine last week when we did a test run. now it’s stuck!

Nextcloud version : 2.3.2.
Operating system and version : Debian / Stretch

Is this the first time you’ve seen this error?:
yes, in previous attempts last week, the uploading/syncing speed was much better

i don’t know how to produce log files to give more info about the set-up. can anyone give me guidance on that?