Intermittent bug: Zapier returns "NaN" instead of formatted date (Lookup field) after a Loop

Hi everyone,

I have a Zap with the following structure:

1. Trigger: new record created in an Airtable table (Table A)
2. Search: find vendors by geographic area
3. Loop from Line Items: one iteration per vendor found
4. Create Record: create a row in another Airtable table (Table B), pulling info from the trigger event
5. Send Email: send an email to each vendor with that info

The issue: in Table A, I have a Formula field called "Date formatée" (Formatted Date) that converts a raw date into a human-readable French string:

 

SWITCH(WEEKDAY({Date de la production}), 0, "dimanche", 1, "lundi", 2, "mardi", 3, "mercredi", 4, "jeudi", 5, "vendredi", 6, "samedi")
& " " & DAY({Date de la production}) & " " &
SWITCH(MONTH({Date de la production}), 1, "janvier", 2, "février", 3, "mars", 4, "avril", 5, "mai", 6, "juin", 7, "juillet", 8, "août", 9, "septembre", 10, "octobre", 11, "novembre", 12, "décembre")
& " " & YEAR({Date de la production})

In Table B, the field receiving this value is a Lookup of "Date formatée".

The date is retrieved correctly in the Trigger (step 1). However, after the Loop (steps 4 and 5), Zapier sometimes retrieves the correct value ("vendredi 18 avril 2026") and sometimes returns "NaN", which then gets written into Table B and sent in the email.

The bug is intermittent with no identifiable trigger condition. The Airtable field itself always displays the correct value — the issue seems to come from how Zapier reads it after the Loop.

Has anyone encountered this before? Could this be a timing issue (Zapier reading the Lookup field before it's recalculated)? Or is there a known limitation with Lookup fields inside a Loop?

Thanks in advance!