AWS Lambda failing with run error "ENOENT: no such file or directory, open '/var/task/bridge.js'" - node.js

Question

I have a Node.js 12.x AWS Lambda that is configured in Serverless Framework to fire when a JSON file is dropped into a specific S3 bucket.
Abcg:
handler: Abcg.handle
reservedConcurrency: 1
iamRoleStatements:
- Effect: Allow
Action: lambda:InvokeFunction
Resource: ${cf:LocTransformer-${self:custom.stageEnv}.ABCFnArn}
environment:
GEO_TRANSFORMER_FN: ${self:custom.var.lambdaFn.LocTransformerABC}
EVENT_SOURCE: ${self:custom.var.eventSourceEquipment}
events:
- s3:
bucket: ${self:custom.var.bucket}
existing: true
events:
- s3:ObjectCreated:*
rules:
- prefix: abcg/
- suffix: .json
When a file is dropped, CloudWatch shows the Lambda invocation failing immediately with the following error:
{
"errorType": "Error",
"errorMessage": "ENOENT: no such file or directory, open '/var/task/bridge.js'",
"code": "ENOENT",
"errno": -2,
"syscall": "open",
"path": "/var/task/bridge.js",
"stack": [
"Error: ENOENT: no such file or directory, open '/var/task/bridge.js'",
" at Object.openSync (fs.js:462:3)",
" at Object.readFileSync (fs.js:364:35)",
" at Object.<anonymous> (/var/task/Abcg.js:10201:60)",
" at __webpack_require__ (/var/task/Abcg.js:20:30)",
" at Object.<anonymous> (/var/task/Abcg.js:59145:5)",
" at __webpack_require__ (/var/task/Abcg.js:20:30)",
" at Object.<anonymous> (/var/task/Aabcg.js:59127:18)",
" at __webpack_require__ (/var/task/Aabcg.js:20:30)",
" at Object.<anonymous> (/var/task/Aabcg.js:44894:15)",
" at __webpack_require__ (/var/task/Abcg.js:20:30)"
]
}
I believe it's failing even before entering my Lambda code because I have some early log statements and these aren't appearing in CloudWatch. And, the project doesn't use Webpack, so I assume this reference in the stack trace is coming from a dependency.
Has anyone seen this error before, in particular the reference to /var/task/bridge.js, which I can't see in my project?