Iterate Field Value and Select by Attribute in ArcMap does not select rows after first iteration

I’m running ArcGIS 10.3 on Windows 10.

I need to find all the Block names and identify the record with the largest area. Then I need to calculate the Species across to the last field. However, it doesn’t seem to do anything after the first iteration.

To do this I set up a basic iteration on field values, using unique values in the Blocks feature class below (which has the same Block names as the input feature class for the "Make Feature Layer" tool), selecting the first BlockId in the Feature Layer and then executing a nested subset selection (SUM_SourceHa=(SELECT MAX( SUM_SourceHa) FROM TestSource_Dissolve)) on the records for that Block to find the instance with the maximum area. Then I simply use that selection to calculate the Species value across to the SpeciesSelect field. The problem is that it calculates this for the first iteration, but not thereafter.

I suspect it’s holding on to the first selection somehow and when it runs the second time, nothing is selected when it’s looking for Block A2 inside the initial selection for A1 and then it gives me the green error saying that it’s empty when it tries to select the maximum. As you can see, I’ve even tried to add the "Clear Selection" operation, but it’s got no affect. Strictly speaking I shouldn’t have to do that as it’s a new selection on each iteration, but I thought it won’t hurt.

What am I missing?