Native SCTP re-transmission and ABORT messages not sent when expected

Issue

• With SCTP tunables like:

net.sctp.rto_max = 500
net.sctp.rto_min = 150
net.sctp.rto_initial = 400
net.sctp.association_max_retrans = 10
net.sctp.path_max_retrans = 5
net.sctp.pf_retrans = 2147483647
net.sctp.hb_interval = 1000

Packet capture of an assoc shows:

 75  19.812263 192.168.0.104 → 10.0.0.140 SCTP 100 HEARTBEAT    # HB to 140 path ACKed in next frame
 76  19.821973 10.0.0.140 → 192.168.0.104 SCTP 100 HEARTBEAT_ACK 

 80  20.765297 172.29.98.104 → 10.0.0.156 SCTP 100 HEARTBEAT    # HB to 156 path ACKed in next frame
 81  20.774524 10.0.0.156 → 172.29.98.104 SCTP 100 HEARTBEAT_ACK
 82  21.105094 10.0.0.140 → 192.168.0.104 SCTP 100 ABORT 

 83  21.184261 192.168.0.104 → 10.0.0.140 SCTP 100 HEARTBEAT    # initial HB to 140 path
 84  21.194010 10.0.0.140 → 192.168.0.104 SCTP 62 ABORT 
 85  22.452250 172.29.98.104 → 10.0.0.156 SCTP 100 HEARTBEAT    # initial HB to 156 path
 86  22.461463 10.0.0.156 → 172.29.98.104 SCTP 62 ABORT 
 87  22.480275 192.168.0.104 → 10.0.0.140 SCTP 100 HEARTBEAT    # 1st unacked HB to 140 path, 1st on assoc
 88  22.489981 10.0.0.140 → 192.168.0.104 SCTP 62 ABORT 
 89  24.024299 192.168.0.104 → 10.0.0.140 SCTP 100 HEARTBEAT    # 2nd unacked HB to 140 path, 2nd on assoc
 90  24.034025 10.0.0.140 → 192.168.0.104 SCTP 62 ABORT 
 91  24.772292 172.29.98.104 → 10.0.0.156 SCTP 100 HEARTBEAT    # 1st unacked HB to 156 path, 3rd on assoc
 92  24.781483 10.0.0.156 → 172.29.98.104 SCTP 62 ABORT 

• We expected 3 heartbeats followed by ABORT, as that is the time in net.sctp.rto_max. Why are we not sending ABORT?