Datanode migration not working

Datanode migration does not work on 6.3.5 properly. Cannot seem to start the migration process - either hangs in the install certificate or directory check.

Manually transferring all existing Opensearch data to a new location and referencing that on Datanode config starts the datanode itself succesfully but the Graylog server does not connect to the datanode - it gets stuck on attempting to connect to the old Opensearch even though all references are deleted from the config. The server seems to read the config file. If I put a blank string to the elasticsearch_hosts, the server complains about it. If the line is commented, it defaults to fallback 127.0.0.1:9200...