files not loaded occasionally due "another thread has locked it for loading"

A small number of my files (around 10 out of 20k) is not loaded each day, with such error being returned after it hits the timeout:

```
error: The conditional request failed
{
"code": "ConditionalCheckFailedException",
"time": "2021-08-23T21:16:14.506Z",
"requestId": "5UCMPG1CQ6QRQAATPJPH8V536VVV4KQNSO5AEMVJF66Q9ASUAAJG",
"statusCode": 400,
"retryable": false,
"retryDelay": 25.6182288251398
}
```

and logging this:

```
debug: Batch is ready to be processed, but another thread has locked it for loading
```

Despite the debug log above, I wasn't able to find any other batches with these files. My configuration is:
- `batchTimeoutSecs: 240`
- `batchSize: 100`
- `batchSizeBytes: ""`

I wonder if anyone else experienced similar issue and whether there's a simple config tweak that could be applied to mitigate this? Thanks.