CodeBuild job triggered by Githab occasionally gets wrong commit

From time to time CodeBuild job which is configured to run on Github PR create/update events is not getting the latest commit, which actually triggered a build. This has happened approximately 5 times today, it is clearly visible since we were changing buildspec file in commits and we saw that builds were using buildspec from previous commit. We don't have developer support plan, but need this reported and fixed to continue using AWS services.