The problem is related to defect # DE473361, to be fixed in next PAPIM release.
CA PRECISION API MONITORING (PAPIM) 3.4.33
EPAgent 10.5. running on CentOS Linux release 7.7.1908 (Core).
1 Backup epaplugins/apim/gatewayOSResource.pl
2 Replace content with the one from attached perl file : gatewayOSResource-testfix.pl
3 Restart EPAgent and verify you can see DISK metrics