Hi.
Yes the issue is sporadic. Right now it just finished 4 successfully run. But this is really kind of weird. other RFC Abap connections are working fine when testing the authorization. This is just for one RFC abap connection.
Looks like I already found the answer. In our EWM test I missed out this parameter (snc/accept_insecure/rfc =1). I will try and check.
Anyways, Thank you Nirmal for the help! 
Regards,
Florence