What you were expecting to happen, and what actually happened:
I bought “Path to Glory I” 2 times for collecting 2 legendary troops that I’m missing. “Spooky Imp” and “Heart of Rage”. With first 30 days I get “Spooky Imp” but on 2nd 30 days I didn’t get the “Heart of Rage”. It gave me “Emperor Khorvash”.
How often does this happen? When did it begin happening?
Happened only once.
Steps to make it happen again
Buy the “Path to Glory I” if your only missing legendary troop is “Heart of Rage”. And wait for 30 days.
As it stands now, Heart of Rage is only available from Vault battles (as a very rare drop) - it is the intended way if you didn’t buy the respective elite pass.
I don’t see why you didn’t get your missing imp though. If a troop is available in Legendary Tasks then it should be available in Path to Glory. They even come out of season, we got like 3 different imps on Monday.
I would focus on the imp and submit a missing reward ticket. Just be sure to explain you still got a troop you already owned, but you should of received the missing imp. Specially since there’s nothing that makes it clear that you shouldn’t of received it.
Misleading on purpose probably but there’s no one to hold them accountable to unfortunately.