External Preview issues with spa_url

The External Preview feature has issues with SPA implementation once used with property placeholders, as described in the documentation below:

https://xmdocumentation.bloomreach.com/library/concepts/spa-integration/configure-hst-for-spa-sdk.html#:~:text=Preview%20URL%20Property%20Replacement

Steps to reproduce:
1. Navigate to path 

/hst:myproject/hst:configurations/myproject/hst:workspace/hst:channel/hst:channelinfo:
  jcr:primaryType: hst:channelinfo

2. Set the property  

org.hippoecm.hst.configuration.channel.PreviewURLChannelInfo_url: http://localhost:3000

3. See the External preview feature works for the specific pages.

4. Change the "PreviewURLChannelInfo_url" property to match the property placeholders as described in the documentation.

5. Observe that the external preview for specific pages get redirected to homepage only.

Current Behaviour:
The external preview doesn't work correctly for specific pages and only gets redirected to the homepage.

Expected Behaviour:

The external preview button and copy preview url options should provide preview for specific pages.