To determine if there is a replication issue in Active Directory we use the following command:
repadmin.exe /showrepl domain.tld | FINDSTR /R /I /C:"fail" >NUL && ECHO 2:Error || ECHO 0:OK
This will output 2:Error when "fail" is in the output of FINDSTR. Problem is that using this in PRTG is always shows 0:OK. This command works fine when running this from the command line.