vcontrold suddenly stops working

[lytenyn]

After a reboot of my machine, suddenly vcontrold stops working.
Adding debug output and sending a simple read command, I see this output:

Sep 29 10:37:31 jupiter vito[261846]: Configuring serial interface /dev/optolink
Sep 29 10:37:31 jupiter vito[261846]: >SENT: 04
Sep 29 10:37:33 jupiter vito[261846]: <RECV: len=1 05 (1390.0 ms)
Sep 29 10:37:33 jupiter vito[261846]: <RECV: received 05
Sep 29 10:37:33 jupiter vito[261846]: >FRAMER: framer_reset_actaddr framer_current_addr = FRAMER_LINK_STATUS(05) (was FFFF)
Sep 29 10:37:33 jupiter vito[261846]: >FRAMER: closed
Sep 29 10:37:33 jupiter vito[261846]: >SENT: 16
Sep 29 10:37:33 jupiter vito[261846]: >SENT: 00
Sep 29 10:37:33 jupiter vito[261846]: >SENT: 00
Sep 29 10:37:35 jupiter vito[261846]: <RECV: len=1 05 (2000.0 ms)
Sep 29 10:37:35 jupiter vito[261846]: <RECV: received 05
Sep 29 10:37:35 jupiter vito[261846]: >SENT: 04
Sep 29 10:37:37 jupiter vito[261846]: <RECV: len=1 05 (2000.0 ms)
Sep 29 10:37:37 jupiter vito[261846]: <RECV: received 05
Sep 29 10:37:37 jupiter vito[261846]: >FRAMER: framer_reset_actaddr framer_current_addr = FRAMER_LINK_STATUS(05) (was FE05)
Sep 29 10:37:37 jupiter vito[261846]: >FRAMER: closed
Sep 29 10:37:37 jupiter vito[261846]: >SENT: 16
Sep 29 10:37:37 jupiter vito[261846]: >SENT: 00
Sep 29 10:37:37 jupiter vito[261846]: >SENT: 00
Sep 29 10:37:39 jupiter vito[261846]: <RECV: len=1 05 (2000.0 ms)
Sep 29 10:37:39 jupiter vito[261846]: <RECV: received 05
Sep 29 10:37:39 jupiter vito[261846]: >SENT: 04
Sep 29 10:37:41 jupiter vito[261846]: <RECV: len=1 05 (2000.0 ms)
Sep 29 10:37:41 jupiter vito[261846]: <RECV: received 05
Sep 29 10:37:41 jupiter vito[261846]: >FRAMER: framer_reset_actaddr framer_current_addr = FRAMER_LINK_STATUS(05) (was FE05)
Sep 29 10:37:41 jupiter vito[261846]: >FRAMER: closed
Sep 29 10:37:41 jupiter vito[261846]: >SENT: 16
Sep 29 10:37:41 jupiter vito[261846]: >SENT: 00
Sep 29 10:37:41 jupiter vito[261846]: >SENT: 00
Sep 29 10:37:43 jupiter vito[261846]: <RECV: len=1 05 (2000.0 ms)
Sep 29 10:37:43 jupiter vito[261846]: <RECV: received 05
Sep 29 10:37:43 jupiter vito[261846]: >FRAMER: framer_reset_actaddr framer_current_addr = FRAMER_LINK_STATUS(15) (was FE05)
Sep 29 10:37:43 jupiter vito[261846]: >FRAMER: could not close (3 attempts)
Sep 29 10:37:43 jupiter vito[261846]: Error opening /dev/optolink

Do I read this correctly that the command is never acknowledged/seen by the heating?
Can this be a hardware failure of my optolink (which is a debug cable I bought, not a custom-built one)?

Any ideas?