Schema refresh failed with Elasticsearch

My current setup is as follows:

I have an ES cluster with 4 nodes, and on a 5th EC2 instance I have redash running (I used the AMI provided by redash).

Everything is within its own vpc on AWS and if I add my ES cluster to redash as a datasource, the connection succeeds!

When I try to refresh the schema, it always says “Schema refresh failed”, however the debug logs show this:

[2020-08-14 13:09:12,079][PID:13][DEBUG][urllib3.connectionpool] Starting new HTTPS connection (1): hostnamehere:9200

[2020-08-14 13:09:12,112][PID:13][DEBUG][urllib3.connectionpool] https://hostnamehere:9200 “GET /_mappings HTTP/1.1” 200 12997
[2020-08-14 13:09:12,119][PID:13][INFO][metrics] method=GET path=/api/data_sources/2/schema endpoint=datasourceschemaresource status=200 content_type=application/json content_length=61 duration=47.81 query_count=6 query_duration=4.34

I have been looking at this for quite a long time, but I can’t seem to figure out what is wrong? :/. Can someone try to help me out?