Session: Error while trying to free lock for ci_session

I'm convinced there's something more at play here. Our app makes heavy use of AJAX and I had to stop logging this message as it fills up our error log. Adding session_write_close helps but does not fix the issue completely. It's not an issue with long running requests I've seen this happen on a request that completed in <100ms.

Relevant thread: https://forum.codeigniter.com/thread-652...=free+lock
Issue on Redis's Github: https://github.com/phpredis/phpredis/issues/816

What version of phpredis are you using? I'm testing a new build of our app on PHP7 and phpredis 3.1.1 and forgot about this issue. I'll do some tests to see if the newer versions of phpredis fix it I was running PHP 5.x and phpredis 2.2.8 while those threads were current.

[edit]
After some quick initial tests I haven't been able to reproduce this error using CI 3.1.3, PHP 7.0 and phpredis 3.1.1. I'll keep an eye on the log and reply if I see it happen again.
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