Worklflow - pass an argument to an email

I have a wf that triggers an email which recently stopped working.

in the script part a variable is defined to be able to read data from a linked table:
let eDodavatel = doo.model.cisloDodavatele.value

In the email part of the wf :

It worked still some days ago but now it terminates with "ReferenceError: eDodavatel is not defined\n
It seems to throw error even in the script itself if I try to print eDodavatel on the next line in the script after let…

I am not sure about setting variable in one part of the script and using it in another part. It is not quarantined to be working.
We recommend to use doo.workflow.runningData to pass data between Workflow steps.