I’m having the same issue and am seeing the same error.
I didn’t add the loaded for soy files (yet) just for js, followed by my babel-loader as per the usage example on the repo: Bitbucket
I even tried just having 1 webpack entry js-file containing
console.log(AJS.I18n.getText('my.global.key'));
But still got the same error about invalid group in regexp.
There’s a similar post here Atlassian Front-End Server utilities
where a babel-related bug was fixed last year so I’m clueless to what the cause is. I’m on versions
"atlassian-webresource-webpack-plugin": "~4.8.0",
"@atlassian/i18n-properties-loader": "~0.7.4",
Maybe @madamczak can shed some light on it? 