Here's my dmesg log after the connection broke (I did not exactly match the moment when it broke) :

$ dmesg | tail -n 50
[ 4128.571844] sd 6:0:0:0: [sdc] Sense Key : Recovered Error [current] [descriptor]
[ 4128.571851] Descriptor sense data with sense descriptors (in hex):
[ 4128.571854]         72 01 00 1d 00 00 00 0e 09 0c 00 00 00 00 00 00 
[ 4128.571865]         00 00 00 00 e0 50 
[ 4128.571871] sd 6:0:0:0: [sdc] Add. Sense: ATA pass through information available
[ 4129.070249] sd 6:0:0:0: [sdc] Sense Key : Recovered Error [current] [descriptor]
[ 4129.070264] Descriptor sense data with sense descriptors (in hex):
[ 4129.070270]         72 01 00 1d 00 00 00 0e 09 0c 00 00 00 00 00 00 
[ 4129.070299]         00 4f 00 c2 e0 50 
[ 4129.070314] sd 6:0:0:0: [sdc] Add. Sense: ATA pass through information available
[ 4129.079873] sd 6:0:0:0: [sdc] Sense Key : Recovered Error [current] [descriptor]
[ 4129.079885] Descriptor sense data with sense descriptors (in hex):
[ 4129.079891]         72 01 00 1d 00 00 00 0e 09 0c 00 00 00 ff 00 00 
[ 4129.079919]         00 00 00 00 e0 50 
[ 4129.079934] sd 6:0:0:0: [sdc] Add. Sense: ATA pass through information available
[ 4129.141741] sd 6:0:0:0: [sdc] Sense Key : Recovered Error [current] [descriptor]
[ 4129.141753] Descriptor sense data with sense descriptors (in hex):
[ 4129.141758]         72 01 00 1d 00 00 00 0e 09 0c 00 00 00 00 00 00 
[ 4129.141786]         00 4f 00 c2 e0 50 
[ 4129.141801] sd 6:0:0:0: [sdc] Add. Sense: ATA pass through information available
[ 4129.208120] sd 6:0:0:0: [sdc] Sense Key : Recovered Error [current] [descriptor]
[ 4129.208134] Descriptor sense data with sense descriptors (in hex):
[ 4129.208140]         72 01 00 1d 00 00 00 0e 09 0c 00 00 00 00 00 00 
[ 4129.208168]         00 4f 00 c2 e0 50 
[ 4129.208183] sd 6:0:0:0: [sdc] Add. Sense: ATA pass through information available
[ 5928.497825] sd 6:0:0:0: [sdc] Sense Key : Recovered Error [current] [descriptor]
[ 5928.497832] Descriptor sense data with sense descriptors (in hex):
[ 5928.497835]         72 01 00 1d 00 00 00 0e 09 0c 00 00 00 00 00 00 
[ 5928.497846]         00 00 00 00 e0 50 
[ 5928.497852] sd 6:0:0:0: [sdc] Add. Sense: ATA pass through information available
[ 5928.979103] sd 6:0:0:0: [sdc] Sense Key : Recovered Error [current] [descriptor]
[ 5928.979118] Descriptor sense data with sense descriptors (in hex):
[ 5928.979124]         72 01 00 1d 00 00 00 0e 09 0c 00 00 00 00 00 00 
[ 5928.979153]         00 4f 00 c2 e0 50 
[ 5928.979168] sd 6:0:0:0: [sdc] Add. Sense: ATA pass through information available
[ 5928.988592] sd 6:0:0:0: [sdc] Sense Key : Recovered Error [current] [descriptor]
[ 5928.988606] Descriptor sense data with sense descriptors (in hex):
[ 5928.988612]         72 01 00 1d 00 00 00 0e 09 0c 00 00 00 ff 00 00 
[ 5928.988641]         00 00 00 00 e0 50 
[ 5928.988655] sd 6:0:0:0: [sdc] Add. Sense: ATA pass through information available
[ 5929.050711] sd 6:0:0:0: [sdc] Sense Key : Recovered Error [current] [descriptor]
[ 5929.050723] Descriptor sense data with sense descriptors (in hex):
[ 5929.050729]         72 01 00 1d 00 00 00 0e 09 0c 00 00 00 00 00 00 
[ 5929.050758]         00 4f 00 c2 e0 50 
[ 5929.050772] sd 6:0:0:0: [sdc] Add. Sense: ATA pass through information available
[ 5929.117093] sd 6:0:0:0: [sdc] Sense Key : Recovered Error [current] [descriptor]
[ 5929.117107] Descriptor sense data with sense descriptors (in hex):
[ 5929.117113]         72 01 00 1d 00 00 00 0e 09 0c 00 00 00 00 00 00 
[ 5929.117142]         00 4f 00 c2 e0 50 
[ 5929.117156] sd 6:0:0:0: [sdc] Add. Sense: ATA pass through information available