I had the same thing happen to the Cardamine lyrata I had, the leaves started getting holes. But that could be the fact that it requires a much cooler temperature. Though I think you have a snail problem.
I do have a few Malaysian Trumpet snails, but they only go up the sides of the tank and are known to be plant friendly. I have some fish, clown loaches, zebra danios, flying fox, and some small "white-tip fin" tetras. I have other plants that have the same sypmtom, but not all...here's the story: I added the plants with the symptoms on Jan. 13th. Parameters were:
pH 6.8, NO3 7, P .4, K 7,Fe .2, Ca 20, Mg 6, Temp 78F
On 1/16 I was leaving on a business trip for a week, parameters were:
pH 7, NO3 5, P .4, K 6,Fe .32, Ca 20, Mg 6, Temp 78F
I returned on 1/21 and all seemed well, some small pin holes, but not as bad as the photo. The filter jammed in my absence and shut off the heater (its built into the filter) and the temp was 72F, parameters on 1/21 were:
pH 6.8, NO3 8, P 0, K 5,Fe .1, Ca 20, Mg 6, Temp 72F
on 1/21, made some adjustemets (added P) to P .5ppm, my tank uses about .1ppm per day, even though the fish food has P.
On 1/22, I suspected the few pin holes I saw was from K defficiency so I upped the K from 5ppm to 10ppm via K2SO4. Next day, the plants looked like the photo! My thought is that the tank is low in K, but limited by P when I went away on the trip, so the K issue wasn't showing up...then when I added the P, it became K defficient since there was enough P.
The other plants that didn't experience the symptoms have been in the tank for months, the previous month I had K levels from 15-40ppm, but the high K was limiting my Ca uptake and showing up as a Ca defficiency, so I lowered the K to 5-10ppm. I think the older plants stored a ton of K and did o.k. on the low levels, but the new plants I added did not have the stores.
It doesn't sound to me like there's really much wrong with your conditions And from what I can see, it doesn't look like the kind of holes you might see if you were short on K.
I'd be willing to bet that the blame lies squarely with your clown loaches. They've been known to damage plants that way. That, or you have some pond snails that you haven't noticed. That's happened to me in the past.