Why can't my clients see anything on their Project Calendar?

There are a couple of reasons why your ClientLink User may not be able to see Events on their Project Calendar -

They don't have access to Calendars - The most common reason your client may not be able to see their Project Calendar and its Events is due to the permissions you've set for your ClientLink Users. Double-check your ClientLink permissions to ensure you have engaged the "Calendar - ClientLink users can view Calendar Events and important Due Dates" option. By default, ConstructionOnline only shows ClientLink Users Calendar Events and other tasks that they have been assigned to, but you also have the option to give them access to the full Project Calendar.
They haven't been added as a Resource to the Calendar Event - Based on ConstructionOnline's default Calendar permissions mentioned in the bullet above, in order to see Events on their Project Calendar, ClientLink Users with default Calendar permissions must be added as an Assigned or Related Resource to the Event. This ensures that the Event will populate on their Project Calendar in the Portal as well as allows you to set up reminders for the Event.