It is strange though. I was going through different threads in here. I come across with a thread Failed to save the enrollment to the server - #8 by Calle_Hedberg , there is a clue from @chase.freeman about the bugs reported on Jira [DHIS2-7865] - Jira.
I changed the Tracked Dashboard from ‘Unlock layout for all users’ to ‘Lock layout for all users’ . It solved a problem at my side. It worth a try.
