I think it maybe a particular problem with some of the newer varieties of Boinc Manager and relates to the extreme length of the CPDN "models" (=work units).
The following worked for me.
- In Advanced View for Boinc Manager Open "Advanced..." -> "Preferences..."
Click on the tab for "network usage"
Set "Connect about every" to 25 days
Set "Additional Work Buffer" to 10 days.
Suspend all other projects.
Update CPDN
A few minutes later Resume all other projects