When you are using context in custom fields and you are going to show this custom field in barchart, the context is not working.
You can create the scenario.
Create custom field CUST1
Use 2 context for different projects. In Project1 field the values A1 and A2. In Project2 field the values B1 and B2.
When you create a filter in jira with contexts appears properly, only show A1and A2 or B1 and B2 BUT when you use the filter created in a BARCHART, appears A1 A2 B1 B2.