Hellebores dying

We bought two healthy, leafy hellebores in the early spring (I think) this year. We planted them into a deep pot, positioned up to a north-west facing wall, so mostly shaded until a little sun later in the afternoon. Over the weeks that followed, both plants’ leaves slowly browned and died. They also suffered from a aphid attack which didn’t help! I thought both plants had died, but about a month ago, one started to grow new leaves. However, a week or so later the new leaves are browning and dying too, from the edges. See the photo, each new leaf begins fine and then starts to suffer. I’m not sure if it’s saveable now, but hopefully we’ll learn something for the future!