Serverless error: serverless-bundle and webpack - The webpack plugin could not find the configuration file

E:\git\serverless-project>serverless deploy --stage ci --verbose
Serverless: Deprecation warning: Variables resolver reports following resolution errors:
- Cannot resolve variable at “provider.environment.MAILER_USER”: Value not found at “self” source
From a next major this will be communicated with a thrown error.
Set “variablesResolutionMode: 20210326” in your service config, to adapt to new behavior now
More Info: https://www.serverless.com/framework/docs/deprecations/#NEW_VARIABLES_RESOLVER

Serverless Warning --------------------------------------

A valid service attribute to satisfy the declaration ‘self:custom.environmentVariables.MAILER_USER.ci’ could not be found.

Serverless: Using configuration:
{
“packager”: “npm”,
“packagerOptions”: {},
“webpackConfig”: “C:\Users\User\AppData\Roaming\npm\node_modules\serverless-bundle/src/webpack.config.js”,
“includeModules”: {
“forceExclude”: [
“aws-sdk”
],
“forceInclude”: null,
“packagePath”: “package.json”
},
“keepOutputDirectory”: false,
“concurrency”: 2
}

Serverless Error ----------------------------------------

The webpack plugin could not find the configuration file at: E:\git\fieldbox-serverless\C:\Users\User\AppData\Roaming\npm\node_modules\serverless-bundle\src\webpack.config.js

Your Environment Information ---------------------------
Operating System: win32
Node Version: 14.17.0
Framework Version: 2.43.1
Plugin Version: 5.1.3
SDK Version: 4.2.2
Components Version: 3.10.1

So it would seem like some path concatenation is happening when trying to get at the webpack.config.js, but I can’t figure out where are the paths misconfigured.

I don’t have any reference in the serverless.yml to webpack at all, all defaults.