Ah, got it. Yeah I think I tried with a very fresh tx ID and that's why it didn't work... although checking again now even Block 511908 (about 33,200 blocks ago now) still shows me the default image. Also tried with the direct URL on several tx hash but giving me the same no-results.
Could it be it can't handle Bech32/native Segwit-related txs? Which is what I'm trying to look at as those are what I'm interesting in at the moment!