Salt-Minion 3006.5 (Sulfur) TypeError: 'NoneType' object is not iterable

I'm running salt-minion version 3006.5 (Sulfur) on my server, and recently I've encountered an issue where the minion becomes unresponsive, and the logs show the following recurring error:

TypeError: 'NoneType' object is not iterable

The full traceback looks something like this:

self.set_exc_info(
File "/opt/saltstack/salt/lib/python3.10/site-packages/salt/ext/tornado/concurrent.py", line 319, in set_exc_info
self._set_done()
File "/opt/saltstack/salt/lib/python3.10/site-packages/salt/ext/tornado/concurrent.py", line 333, in _set_done
for cb in self._callbacks:
TypeError: 'NoneType' object is not iterable

I've tried to investigate the issue, but I'm struggling to find the root cause. I suspect it might be related to the Tornado library or perhaps some configuration issue, but I'm not sure where to start looking.

What I've done so far:

1. Checked all relevant configurations to ensure no values are None.
2. Verified that all dependencies are up to date.
3. Restarted the salt-minion service multiple times, but the issue persists. System Details:

• Salt-Minion Version: 3006.5 (Sulfur)
• Python Version: 3.10

Has anyone else encountered a similar issue with this version of Salt, and what steps did you take to resolve it? Any guidance on debugging this further would be much appreciated.

Thanks in advance!

That is the same error as described in this issue, which has been fixed in 3006.7