Index matches multiple legacy templates

I have followed [this guide](https://docs.graylog.org/en/4.0/pages/configuration/elasticsearch.html#custom-index-mappings) in the documentation in order to setup as custom mapping for a few fields.

The custom mapping works fine, however I am seeing occasional `Warnings` in the logs as follows :
```
2021-05-05T12:20:21.676+01:00 WARN [RestClient] request [PUT http://10.10.10.10:9200/graylog_3969?master_timeout=30s&timeout=30s] returned 1 warnings: [299 Elasticsearch-7.10.2-747e1cc71def077253878a59143c1f785afa92b9 "index [graylog_3969] matches multiple legacy templates [graylog-custom-mapping-7x, graylog-internal], composable templates will only match a single template"]
2021-05-05T14:02:21.692+01:00 WARN [RestClient] request [PUT http://10.10.10.10:9200/graylog_3970?master_timeout=30s&timeout=30s] returned 1 warnings: [299 Elasticsearch-7.10.2-747e1cc71def077253878a59143c1f785afa92b9 "index [graylog_3970] matches multiple legacy templates [graylog-custom-mapping-7x, graylog-internal], composable templates will only match a single template"]
```
Are these warnings concerning ? If yes, any suggestions on how to resolve them ?

## Environment
* Graylog Version:
* Java Version: 1.8.0_292
* Elasticsearch Version: 7.10.2
* Operating System: Ubuntu 20.04 Server