A workaround that works over here is to move the whole AppleScriptObjC part into a script library
Embedded Smart Rule script:
on performSmartRule(theRecords)
tell application id "DNtp"
repeat with theRecord in theRecords
set theText to plain text of theRecord
script "Skript-Library - displayAlert"'s displayAlert(theText)
end repeat
end tell
end performSmartRule
Script library:
use AppleScript version "2.7"
use framework "Foundation"
use scripting additions
on displayAlert(theText)
tell application id "DNtp"
try
activate
display alert theText
on error error_message number error_number
activate
display alert "Error: Handler \"displayAlert\"" message error_message as warning
error number -128
end try
end tell
end displayAlert