ovs-ofctl dump-ports shows question marks ('?') in OVS DPDK environments in Red Hat OpenStack Platform

Issue

ovs-ofctl dump-ports shows question marks (?) in OVS DPDK environments in Red Hat OpenStack Platform.
What is the reason for ? across some of the statistics in the output of ovs-ofctl dump-ports.

For example:

[root@overcloud-compute-0 openvswitch]# ovs-ofctl dump-ports br-int
OFPST_PORT reply (xid=0x2): 6 ports
  port  6: rx pkts=105, bytes=8828, drop=0, errs=0, frame=?, over=?, crc=?
           tx pkts=49, bytes=7978, drop=4, errs=?, coll=?
  port  1: rx pkts=205, bytes=32427, drop=?, errs=?, frame=?, over=?, crc=?
           tx pkts=315, bytes=26246, drop=?, errs=?, coll=?
  port  7: rx pkts=103, bytes=8688, drop=0, errs=0, frame=?, over=?, crc=?
           tx pkts=42, bytes=7182, drop=9, errs=?, coll=?
  port LOCAL: rx pkts=0, bytes=0, drop=0, errs=0, frame=0, over=0, crc=0
           tx pkts=35, bytes=3600, drop=0, errs=0, coll=0
  port  2: rx pkts=0, bytes=0, drop=?, errs=?, frame=?, over=?, crc=?
           tx pkts=35, bytes=3480, drop=?, errs=?, coll=?
  port  5: rx pkts=104, bytes=8730, drop=0, errs=0, frame=?, over=?, crc=?
           tx pkts=48, bytes=8299, drop=4, errs=?, coll=?
[root@overcloud-compute-0 openvswitch]# ovs-ofctl show br-int
OFPT_FEATURES_REPLY (xid=0x2): dpid:0000928a21233745
n_tables:254, n_buffers:256
capabilities: FLOW_STATS TABLE_STATS PORT_STATS QUEUE_STATS ARP_MATCH_IP
actions: output enqueue set_vlan_vid set_vlan_pcp strip_vlan mod_dl_src mod_dl_dst mod_nw_src mod_nw_dst mod_nw_tos mod_tp_src mod_tp_dst
 1(int-br-link): addr:5e:1a:76:19:02:1f
     config:     0
     state:      0
     speed: 0 Mbps now, 0 Mbps max
 2(patch-tun): addr:8e:30:8c:27:02:e8
     config:     0
     state:      0
     speed: 0 Mbps now, 0 Mbps max
 5(vhubd172106-73): addr:00:00:00:00:00:00
     config:     0
     state:      0
     speed: 0 Mbps now, 0 Mbps max
 6(vhuce3d2be0-6e): addr:00:00:00:00:00:00
     config:     0
     state:      0
     speed: 0 Mbps now, 0 Mbps max
 7(vhue8241644-29): addr:00:00:00:00:00:00
     config:     0
     state:      0
     speed: 0 Mbps now, 0 Mbps max
 LOCAL(br-int): addr:92:8a:21:23:37:45
     config:     PORT_DOWN
     state:      LINK_DOWN
     current:    10MB-FD COPPER
     speed: 10 Mbps now, 0 Mbps max
OFPT_GET_CONFIG_REPLY (xid=0x4): frags=normal miss_send_len=0