ISR4321 is IOS-XE device and doesn't support CISCO-POP-MGMT-MIB (http://www.cisco.com/c/en/us/td/docs/ios/ios_xe/3/release/notes/asr1k_rn_3s_rel_notes/asr1k_rn_3s_mibs.html). cpmDS1ActiveDS0 is oid from that mib. That's why it doesn't work on your new device.
Try o search here for oids - http://tools.cisco.com/ITDIT/MIBS/servlet/index
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