“show tag values” yields different results between CLI and web API

I'm getting different results depending on whether I query using the CLI or the API.

__Steps to reproduce:__

Using the CLI:

```
use mydb
show tag values from "mymeas" with key = "description"
```

Using the web API:

```
curl -G 'http://localhost:8086/query?db=mydb' --data-urlencode 'q=show tag values from "mymeas" with key = "description"'
```

__Expected behavior:__
I expected to get the same list of tag values.

__Actual behavior:__

146 results using the CLI
40 results using the API

Some values are missing when using API and I don't get why.

(As a consequence, Grafana doesn't show all the available tags in its dropdown menu.)

__Environment info:__

* System info: Linux 4.19.0-13-cloud-amd64 x86_64
* InfluxDB version: InfluxDB v1.8.4

Am I misunderstanding something?

[Also asked on SO](https://stackoverflow.com/q/67717885/4653485).

The issue names no source files or tests. Reproduce the CLI and web API queries against InfluxDB v1.8.4, then trace their separate query paths and compare the returned tag values. Done means both interfaces return the same complete list, with regression coverage for the API response.

Written by the indexing model from the issue text.