Hello & welcome, @guifsdev
First, you need to understand how Seamly2D saved your pattern file. If you open the pattern file in a text file, you will see that it saves the version & name first, then the Curstom Variables, then the 1st board (with all the nodes, curves & lines), 2nd board, etc. & lastly the pattern Details.
And when a pattern is read from a file, it looks at the file in this exact order. Presently, it can’t look ahead to see what was created later.
So affectively, it’s no use to use anything in the custom variables that is in the pattern, because they are save afterwards in the list and will always revert to 0.
It would be better to use a fixed value on both the armhole and the sleeve to place the node in the same place, or use a formula that refers to a measurement in the measurement file.