Bash 4: unexpected EOF while looking for matching `)'

This very simplified version of my script

#!/usr/bin/env bash
example="$(bash -rs <<'BASH' -- 'This has been executed in restricted shell'
  echo "$1"
BASH
)"
echo "$example"

is executed without problems on a system with bash version 5.1.4. However, on another system with bash version 4.0.44, I get the error

line 2: unexpected EOF while looking for matching `)'

If I change the script to

#!/usr/bin/env bash
example="$(bash -rs <<'BASH'
  echo 'This has been executed in restricted shell'
BASH
)"
echo "$example"

or

#!/usr/bin/env bash
bash -rs <<'BASH' -- 'This has been executed in restricted shell'
  echo "$1"
BASH

it also works on the system with bash version 4. Does anyone have an idea what could be the reason?