Here is the error messages the indicator date time gives me on 20.04 and recently started on my 19.10 machine as well
** (process:9862): WARNING **: 09:19:40.210: could not find the desktop file for 'org.gnome.Calendar.desktop'
(process:9862): Indicator-Datetime-WARNING **: 09:19:40.405: Unrecognized TZID: 'Etc/Utc'
(process:9862): Indicator-Datetime-WARNING **: 09:19:40.407: Unrecognized TZID: 'Etc/Utc'
(process:9862): Indicator-Datetime-WARNING **: 09:19:40.421: Unrecognized TZID: 'Etc/Utc'
**
Indicator-Datetime:ERROR:/build/indicator-datetime-SpDTj1/indicator-datetime-15.10+20.04.20200217/src/date-time.cpp:171:GDateTime* unity::indicator::datetime::DateTime::get() const: assertion failed: (m_dt)
Bail out! Indicator-Datetime:ERROR:/build/indicator-datetime-SpDTj1/indicator-datetime-15.10+20.04.20200217/src/date-time.cpp:171:GDateTime* unity::indicator::datetime::DateTime::get() const: assertion failed: (m_dt)
Aborted (core dumped)