Using the GSS interface with Sysview Performance Management Option for Db2 for z/OS (IDB2), and noted
many messages: GSS ERROR: Invalid PLIST, "GSST" is missing IMOD ERROR RETURN CODE 20 REASON 31 in the Data Collector.
This seems to only be occurring on the IDB2 Data Collector that monitors a heavily used Db2 subsystem.
The 'IMOD ERROR RETURN CODE 20 REASON 31' indicates the GSS MAXXREQ table ran out of room to handle the volume of IMOD requests.
To address this condition, increase the GSS runparm values for EVENTS and MAXXREQ to: EVENTS 32767 MAXXREQ 8000.
Also, you will want to make certain the GSS 14.0 PTF RO42823 is applied.