In that case there would be a dump in ST22.
Same user context call backs also dont check S_RFC by default.
I place my bets on the application server switch where the IGS is started and s_log_com because of the SAP_ALL working.
Otherwise I would normally have tipped on the SMGW restrictions. Mindlessly asetting param gw/reg_no_conn_info too high is the most common cause of problems there...
Cheers,
Julius