I guess we would need more information as this is not reproducible for at least me. can you attach an example or tell more about the tests and settings you are using and if you are using any other column properties in the data table?
from what you posted the only reason might be there are two points with the same value in the data table. I doubt I can find another reason without taking a look at the data and try to replicate the analysis. Sorry.
May you want to Tables menu -> Anonymize, if you cannot share it otherwise?
I am not able to duplicate. This is what I get for the relevant portion of the picture:
Perhaps there is a step that you are doing that is being missed? Which version of JMP are you using? Windows or Mac?
Win 10 pro
1. I select the column for labeling
2. Then choose Row Label
3. Also I need to test this point
and by this step Double Labeling switches on.
Please describe your algorithm.
I perform exactly the same steps you provided above, but still just get one label
I realy don't know where this comes from. May reinstall JMP and see if this still exists. I doubt Tech Support will be of much help here as it seems it is hard to reproduce or just on your machine. However, you can ask them if there has been such a case in the past.
Have you tried the same on another machine or at a collegues desk? If they also cannot reproduce the behaviour with your file, it has - most likely - something to do with your machine.