influx backup --bucket-id a68a42429e903768 /tmp/backuptest/ crashes with Error: An internal error has occurred

__Steps to reproduce:__

```
influx backup --bucket-id a68a42429e903768 /tmp/backuptest/
```

__Expected behavior:__

```
2020-12-07T11:32:41.275063Z info Backup complete {"log_id": "0QwFRrXG000"}
```

__Actual behavior:__

```
2020-12-07T11:29:38.279432Z info Backing up shard {"log_id": "0QwEsGU0000", "id": 2268, "path": "20201207T112238Z.s2268.tar.gz"}
2020-12-07T11:29:48.159171Z info Backing up shard {"log_id": "0QwEsGU0000", "id": 2283, "path": "20201207T112238Z.s2283.tar.gz"}
2020-12-07T11:29:53.397807Z info Backing up shard {"log_id": "0QwEsGU0000", "id": 2285, "path": "20201207T112238Z.s2285.tar.gz"}
Error: An internal error has occurred.
See 'influx backup -h' for help
```

It's always shard 2285.

__Environment info:__

* Linux 4.15.0-72-generic x86_64
* Ubuntu 18.04
* Installed from `deb https://repos.influxdata.com/ubuntu bionic stable`
* Influx version: Influx CLI 2.0.1 (git: 37cc047133) build_date: 2020-11-11T03:53:31Z
* `aptitude show influxdb`: 2.0.1

__Config:__

I don't know what to post here. `dpkg-query -L influxdb` shows `/etc/influxdb/influxdb.conf` is the config file, but that is al old one from 2019. Even `influxdb.conf.dpkg-dist` is old: jul 10 2020. They all refer to the old data dirs, that are no longer there (like `/var/lib/influxdb/data`)

There's `/var/lib/influxdb/.influxdbv2/configs`, but it only contains:

```
[default]
url = "http://localhost:8086"
token = "removed=="
org = "my-org"
active = true
```

__Logs:__

There are none. `journalctl -f -u influxdb` shows nothing when the error occurs.

There are no flags for verbosity.

The produced tgz file is empty.

I can't figure out how to set the [log level](https://docs.influxdata.com/influxdb/v2.0/reference/config-options/#log-level). No matter where I put `config.toml` with `log-level = "debug"`, I only see `lvl=info` in `journalctl -f -u influxdb`. The data dir is in `/var/lib/influxdb/.influxdbv2/`, so that leads me to conclude `/var/lib/influxdb/config.toml` should work, but it doesn't.

(is there no way to configure a log file BTW?).

The bucket is 7 GB big, so it's kind of big to send, and it can contain sensitive data.

I don't know what else to give.

Start by reproducing `influx backup --bucket-id a68a42429e903768 /tmp/backuptest/` and inspect the handling of shard 2285, where the command consistently fails. The issue names no source file or test, so trace the backup CLI entry point and shard-processing path. Done means the command completes and produces a non-empty backup archive instead of the internal error.

Written by the indexing model from the issue text.