It seems to be happening since December, giving output:
Can't open /srv/xenon/logs/hourly/2020-01-08_20.excimer.load.log: No such file or directory at /usr/local/bin/flamegraph.pl line 491. ERROR: No stack counts found
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I am not advocating to 2> /dev/null, but this seems like a real issue you may want to fix or workaround. I saw some other tickets related to performance logging and monitoring, but no mention of this.