Custom Mode Calculation Error - Is there a limit on the number measures that can be used in a calculation?

I am working in Custom Mode and building a calculation, but after applying my calculation, I keep getting “An error has occurred when querying the data”

I noticed not all of my measures have a variable assigned to them. It looks like whenever I add more than 5 measures, the additional measures do not get a variable assigned and the box is blank.

Does anyone know if there a limit to the number of measures that can be used when writing the expression for a calculation?

Here is what I am trying to do, but it is not working. Notice the measures after “e”, do not get a variable assigned.

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My understanding is its a max of 5 hence why measures after “e” are not assigned a letter.