Serverless 1.28.0 cannot read stage variables from a yml file

I updated my serverless project to latest version (1.28.0) and I can’t deploy my project anymore. The problem is the sls cannot read my stage variables referred in a yml file located in a folder (stage_vars) in the root directory. I defined all the stage variables like “awsProfile” and “envName” in a file like “dev.yml” (located in the “stage_vars” folder) and referring them in the serverless.yml file for example:

stageVars: {file(stage_vars/{opt:stage}.yml)}

profile: ${self:custom.stageVars.awsProfile, self:custom.defaultAwsProfile}
variableSyntax: ‘${((((self|opt):)|file)((?!${).)+?)}’

If I provide the profile name directly as a string it would work but it is not working using the above syntax. Am I missing something in the new version?