Your mistake is in the attempt to read a Table 1 field from a row coming from Table 2. CurrentValue within your deref is set by the inner FormulaMap iterating over Table 2. Even the color coding tells you this:
You lose outer CurrentValue when you nest iterating contexts. This is a known issue.
Here’s a megathread on that, featuring some workarounds (snoop for my answers):
And here’s my tutorial for one bulletproof pattern how to approach similar scenarios, when you need to iterate with nested loops in a button:
