Hi,
First you verify that the calculation is actually triggered by using adding e.g. the following to your rule:
BRApi.ErrorLog.LogMessage(si, "YES!")
You check the error log and if you find your "YES!" in there, you have that confirmed.
Then you just create a cube view with a valid input cell using A#2A900A01 and select the target cell's POV using right click >> 'Cell POV Information'. Copy the non-data unit part, which will look something like this:
A#2A900A01:F#CHI:O#Forms:I#None:U1#None:U2#None:U3#None:U4#None:U5#None:U6#None:U7#None:U8#None
Use this in your formula and test. This should put data on that single cell in your cube view. Then you take away one dimension after another from your formula until you end up with your original string A#2A900A01:U1#None:U3#None:U5#None:I#None:F#CHI. Run the calculation after each one and verify the data is still in your CV. At some point you should be able to see where it does no longer work as expected.
There are more ways, but I hope this is the fastest one for you.