Comment 5 for bug 1722455

As a workaround:

in ~/.config/evolution/sources create a file calendar.source

$ touch calendar.source

edit it:

[Data Source]
DisplayName=<Calendar>
Enabled=true
Parent=webcal-stub

[WebDAV Backend]
AvoidIfmatch=false
CalendarAutoSchedule=false
DisplayName=
EmailAddress=
ResourcePath=</Enter/your/CalDAV/URL/here>
ResourceQuery=
SslTrust=

[Offline]
StaySynchronized=true

[Calendar]
BackendName=caldav
Color=#6666CC
Selected=true

[Authentication]
Host=<your.mailhost.com>
Method=plain/password
Port=80
ProxyUid=system-proxy
RememberPassword=true
User=<YourUserName>
CredentialName=

[Security]
Method=none

[Refresh]
Enabled=true
IntervalMinutes=1

<can be substituted to suit your requirements>