Ok this has been fixed.
Note: if you wanted to jump directly to a transaction (your transaction), you can just search for that TX ID and it will take you straight there:
Preturnio returns a result here because there is an OP_RETURN inside that transaction and Preturnio indexes all OP_RETURNs. As I mentioned below, the '/' delimiter wasn't part of the search index regex analyzer - so if you searched for 'substack' you'd see your OP_RETURN transactions - but 'darthcoin' wasn't registering as a match.
I've updated the search index regex and so now 'darthcoin' will return results because the analyzer will include specific words in between '/' and '.'
(Turns out that free form text indexes are tricky to configure :))
Thanks for pointing this out and giving me an opportunity to tweak the index.