This got logged today.
I've got ten others like it. Same error, all from keepalive, all guests. I
suspect that they are spiders. No file is referenced.
PHP version is 7.1.5.
Sounds similar to this one as well ... https://github.com/elkarte/Elkarte/issues/2933 have not been able to isolate the issue :(
Just a wild hunch: a delay might produce that result.
Could it be related to http://www.elkarte.net/community/index.php?topic=3945.0 ?
Maybe ... I guess I can comment it out and see what happens :D
Doing that really pissed it off .... constant stream of errors, not just on xml style requests
LOL
Well, at least it was not entirely my fault. xD