Is it possible to restart the listener on 5009, without rebooting the AP?
Not by any means Apple has given you, because that means you have no access to the TC controls at all. But did you try a soft reset??
Are there known reasons for the listener to stop working?
None that I can think of.. once it is off it will prevent any access at all. A firmware upgrade won't do that.
I assume the security issues alluded to in older posts have been mitigated by newer firmware versions.
When Apple discover a security hole they patch the firmware. Any firmware security update should fix that issue plus any outstanding that have not yet been fixed. Of course Apple do not release a whole lot of info about what they do.
If any particular update is so important as to make it essential to security the NVRAM setting is altered to change the min firmware level.
The latest update for example to 7.6.9 or 7.7.9 depending on the series is still reversible. In fact in the Gen 4 TC the list of firmware is still very long. So Apple still consider the security ok.. even if some particular issue is not fixed. So the latest one fixed the issue with KRACK but it is so specific that upgrade is not essential and lots of people do downgrade for various reasons.
Sorry to say but I think a TC where the control port has failed needs replacement. There is no repair method.
As per usual, if you are in warranty or have applecare or applecare still possible and the TC is less than 2 years old.. get Apple to replace it.
Email me directly and I can help you get console access maybe. rayhav@gmail.com
You might be able to get access to the errors and find out if something has failed.. but it will not tell you why.. nor will it fix the problem.. although you might be able to restart the daemon without actual power cycle.
How old is the TC that goes bad?
How long does it take for the TC to fail after a reboot?
The normal process I would try would be a
1. Factory reset
2. Firmware downgrade
3. Factory reset again
4. Reconfigure using tight SMB rules.
If you get no improvement after doing that then you can pretty much sure it is going to need replacement.