I'd say this is a mistake in the planner.

@Nanja, this is something for the next planner update, I suppose.

Edit: I just checked in my own app and that train doesn't have any remarks in the Interrail app. Maybe that was corrected with today's update?

@reinsch9z  I can say that the trains of Die Länderbahn alias “Alex” are within the passnetwork if your app still say it´s not i assume you have an outdated app as mine says since few weeks that they are covered :)

I used them already with Interrail pass :)

Just to confirm, it used to be mentioned as not being included but this has recently been adjusted as Die Länderbahn is indeed covered by Eurail/ Interrail. Cheers, 

Die Länderbahn CZ also operate some local services around Chomutov. I just had the pass refused on one of these so it’s not as simple as saying DLB is covered by the pass. Fortunately I was only going two stops and the lady didn’t bother charging me.

@desperado should be included in the pass, where the German Rail Fare for local trains is valid “Deutschlandtarif”, 

In Czech Republic only CD, Regiojet and LeoExpress accept Interrail/Eurail if I am not wrong.

Like Arriva CZ (a company of DB) do not accept it. Maybe it is the same here for trains of Länderbahn CZ (a company of Netinera - part of Trenitalia). 

The app / web journey planner show the “Die Länderbahn CZ” trains as included (look up Chomutov to Jirkov for example). If, in the app, you do “more” → “Rail network guides” → “Czech Republic”, “Die Länderbahn CZ” is not listed, either as included or as excluded. It’s just missing.

@desperado 

Please report this to Customer Support using the form below so that they can check and if needed make updates.

https://eurail.zendesk.com/hc/en-001/requests/new