Unable to sync across devices

What I did: downloaded app on desktop & laptop (both Mac) and iPhone 8+, confirmed that both machines have iCloud Drive on, and the Agenda app is also turned on to sync.

What happened: My iPhone and desktop ARE syncing, but the laptop is NOT.

Are you sure iCloud drive is really enabled on the laptop, and that the laptop is logged into the same iCloud account as the other devices? Finally some corporate networks block iCloud drive, make sure this is not the case here too.