You don't always see the slime trails. Apparently the really little "snot like" slugs do the worst damage :-( At least if it's in a pot it should be easy to sort out.

Thanks, I will look more closely and put some slug pellets in the pot. Hopefully that will sort them out!

Vine weevil adults also make holes in leaves

Thank you 2ndhand! I've been giving it some thought about it being slugs. They usually nibble from the sides of leaves whereas the leaves on my plant actually has lots of holes.

Dicentra spectabilis flower fairly early in the season, and usually have disappeared completely by midsummer, so it could just be dieing back, which is quite natural,
they are a quite shortlived perennial, and should be in a shady position, Derek.

Thank You DerekM - the pot is in a east facing position so only gets early morning sun. There is no where in my garden that it wouldn't get some sunshine.

Never thought of that Derek, especially as mine are always coming into their own at the end of June to mid July. I forget that they are normally a lot earlier. :-)