Error while crawling LOB contents. ( Error caused by exception: Microsoft.BusinessData.Infrastructure.BdcException The shim execution failed unexpectedly - Exception has been thrown by the target of an invocation..: System.Net.WebException The underlying connection was closed: Could not establish trust relationship for the SSL/TLS secure channel.; SearchID

Error while crawling LOB contents. ( Error caused by exception: Microsoft.BusinessData.Infrastructure.BdcException The shim execution failed unexpectedly - Exception has been thrown by the target of an invocation..: System.Net.WebException The underlying connection was closed: Could not establish trust relationship for the SSL/TLS secure channel.; SearchID 

The issue with the certificates not being recognized as trusted in the SharePoint Farm. To resolve this:

• Go the the Certificate, Click on Certificate Path 
• Select the Root Certifcate, Double Click on it
• Click on Details 
• Click on Copy to File
• Save the file
• Now Go to SharePoint > Security > Manage Trust
• Create a New Trust >  Import the Root certificate
• Click oK
• Run and iisreset on the SharePoint servers
• Run a full crawl now

Issue resolved for me.

Check the ULS to find more information , may have to switch on verbose extended logging, but generally speaking, the cause of the issue will be the certificates.