RFC Connection timeout

From time to time, a background job is failing requesting data from another system via RFC,

Y/RSC/RFC_AD1_000:Time limit exceeded.

Requesting the data takes always 20 Minutes, regardless if it fails or not. As a first step, i went to SM59, selected the RFC connection and under special options i entered 1800 secs as timeout, not the gateway value. 1800 secs is half an hout, but still sometimes(!) the job crashes after 20 Minutes. As a second step i selected to disable the time out for this connection, but the job still crashes, not always, but from time time.

What else di i have to consider to get rid of this time outs completly?