readFileFromWorkspace doesn't not update the shell step if the referenced file content has changed. I have checked that Action for existing jobs and views -> Ignore changes box is NOT ticked.
Exemple:

step {
     shell(readFileFromWorkspace("/apps/tools/scripts/myscript.sh"))
}

myscript.sh content:

#!/bin/bash
echo Hello world!

The first time I build, the jobs are created correctly with the matching shell step content:

#!/bin/bash
echo Hello world!

If I change the script myscript.sh:

#!/bin/bash
echo Hello guys!

I build again I still get the previous content in the step:

#!/bin/bash
echo Hello world!