I have the same issue except my data is already int32 for both of my fields. It is a simple divide of sum(field1)/sum(field2). both field1 and field2 are integers and for the life of me I cannot figure out why its not showing. The only way I can get it to show up is if I do not sum it but then of course the numbers are incorrect. Here is a sample:
There should be both a yellow line and a black line. What is even more odd is that the data point shows up but the line does not.