Conditional Formatting breaks with "forced" zero

I have a relatively simple matrix display with a single measure, on which I am using Conditional Formatting. 

Threshold Count UC-MV = 
var __ThisType = SELECTEDVALUE(Event_Tbl[UC])
var __Cnt = SWITCH(__ThisType,
            "MV-C", COUNTROWS(FILTER(SUMMARIZE(DimValves, DimValves[Valve], "Cnt", [Movement-Close]), [Cnt] > 0)),
            "MV-O", COUNTROWS(FILTER(SUMMARIZE(DimValves, DimValves[Valve], "Cnt", [Movement-Open]), [Cnt] > 0)),
            "UC-C", COUNTROWS(FILTER(SUMMARIZE(DimValves, DimValves[Valve], "Cnt", [Uncommanded-Close]), [Cnt] > 0)),
            "UC-O", COUNTROWS(FILTER(SUMMARIZE(DimValves, DimValves[Valve], "Cnt", [Uncommanded-Open]), [Cnt] > 0))
                        
) + 0  // +0 added here to force a value to be shown
return __Cnt

The measures inside this measure are of the form

Movement-Close = COUNTROWS(FILTER(Event_Tbl, Event_Tbl[UC]="MV-C"))

(This has to be 4 separate measures based on user-requirements for the report - a story for another day)

(Also, do not want to add "+0" here, as a different matrix will show more detail and we want to leave blanks to be blanks in that matrix)

I am doing conditional formatting based on the "Train" column, which is a parent of DimValves.

Event_Tbl from the inner measure is a child of DimValves.

When the measure has a non-zero value everywhere, conditional formatting works. 

But if the measure returns 0 (meaning it would return BLANK if I hadn't added the "+0" line), the columns with zero are not formatted

I have tried both with Rules based on the the Train column (Text = Train 1, etc), and using "Field Value" with a measure that returns the proper color based on the value of Train; neither works for the zero columns.

Is there something about the measure that is breaking the conditional formatting, or possibly a bug in Power BI itself?

I should also mention I have tried without the forced 0 and using "Show items with no data", but that supresses the blanks completely.

The report is difficult to anonymize, as would providing sample data, but if there is nothing obvious in the code above, I can try to put together a sample showing the behavior.

Thanks in advance,

David