This has already been raised here. So it’s on the radar, but isn’t a high priority at the moment 
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We’re in exactly the same boat at the moment, hopefully this is fixed soon.
I’m fairly certain you can record arbitrary information against PR comments, so it should be possible to record which build a comment is for. It’s a shame that the code involved isn’t on GitHub, but I guess is makes sense as it’s in the paid-for part of SonarQube…