I am having problems with displaying data from external data source in Lightning. I have a connection to SharePoint Online while using Indirect Lookup relationship to match external data with Accounts.
Everything works fine in Classic (data are matched as expected, displaying in Related List correctly), but after going into Salesforce Lightning, in some cases, there aren't any data present in the Related List.
I've found this known issue: https://success.salesforce.com/issues_view?id=a1p3A000000erW7QAI&title=related-list-for-external-object-not-showing-any-records-in-lightning
As you can see in the Known Issue page above, there isn't any fix yet and the only workaround is to check how the data are handled by OData producer (SharePoint) or if the External Column Name is/isn't Case Sensitive.
Is it possible to check or modify the OData that are passed from SharePoint to Salesforce? Do you have an experience with this problem?
I don't have any experience with this specific problem, but it would seem there are a number of things you could do to help yourself diagnose how to deal with it in your code. First, you don't say if you're using OData 2 or 4 (read-only vs read-write). I'm going to assume you're only reading the data. Your configuration should be readily available for you to review in setup for the field types.
If its working fine in Classic but not in Lightning, that should tell you something about the nature of your problem by collecting some more information on what you're doing differently in Lightning than what you're doing in Classic.
Are you using the Related List Component in Lightning for example as opposed to the related list that's available on the Detail layout? The Detail layout is common between both Classic and Lightning. If you add the related list for this item to your Detail layout on a Lightning Page and don't rely on the Related List Component to display it, does that solve your problem? I strongly suspect it might due to the way the Related List Component is coded in JS as a Lightning Component.
Another thing that might be worth trying is to use the Related Object List component to see if it displays any differently (I wouldn't expect it to, but it might). There's also a free Lightning Component on the App Exchange Called myDynPro that I've been working with that might also do what you're trying to accomplish without needing to write any code. It has a great deal of flexibility and may just do the trick for you.