curl -XGET 'host_A:9200/_cat/health?v&pretty' should be curl -XGET 'host_B:9200/_cat/health?v&pretty'. You may want to try with local/public IP of that server, to exclude the possible problem that the host name isn't working correctly
network.host: 0.0.0.0 should actually work, according to this answer: https://stackoverflow.com/questions/...
your custom layout newsletter_subscriber_block.xml should look like below:
<page xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:View/Layout/etc/page_configuration.xsd">
i have also faced this issue. its not a js error or anything. if you have saved your login credentials in your browser means, its automatically storing in paypal cofig. i just removed the configs. its working