Apply filter to formula

So this measure reads seems like you're trying to sum the count of distinct table IDs, but only while using the [Event Title] column?? It's like you're asking "How many tables do we have? Sum all those numbers you just told me! Oh, and the only data I'm giving you to work with is the list of Event Titles!" That seems not right to me.  

I would start from scratch and re-write it like this for 2019:

# Count = CALCULATE( DISTINCTCOUNT('Table'[ID#]), FILTER('Table', YEAR('Table'[Date]) = 2019) )

Depending on what sort of visual you're putting this in, you may not have to specify all this.  If it's in a column chart with the year as an axis, PowerBI will automatically do this filtering for you if you set up the value of the bar to be a distinct count of IDs. More info on how you're using this and/or table structure would be helpful if this isn't the result you're looking for.