I am aware of this and I know we supported charts with one indicator as filter in version 2.11.
The reason why we didn’t implement support for it in 2.12 is that the semantics seems to be wrong: One cannot really specify an indicator as a filter to other data dimensions, since an indicator is a construct on top of the data element dimension and might contain multiple data elements. Yes I know that one could make an exception and use a single indicator as a filter, but it would in practice be more of a dimension selection and it feels like a hack. This is of course up for discussion, but at the moment you will need to redesign your chart and define your indicator(s) as series or categories.