Arghhhh ..... just lost my whole post. Ahem, so what I meant to say was .......
could be anything. This happens to me on occasion and it IS frustratng. Sometimes, well ~ plants just die. Life over.
Take the Case of the Two Hostas. Two hostas, same variety, bought on same day, same store. Planted side-by-side, same bed, same soil. One got HUGE, I mean massive. The other never did a thing, so I finally just moved it out to another bed.
Who knows? But I do a lot of moving around. If something isn't doing well, or is taking over ~ out it goes.
My main problem since being in KY is that things just get too darn big. My butterfly bushes look like minivans and are choking and crowding everything else out. Artemisia? Arghhhhh ..... you had better like it.
If you try something different, sometimes it fixes the problem and sometimes not. Boy, am I a lot of help on this or WHAT??

Most plants are affected by weather more than other plants. My plants crowd each other. I found a lot of people I have talked with have had unusual experiences with their plants this year because of the weather. Hard winters or mild winters can cause plants to respond differently. We had a hard winter and some plants bloomed more this year than any other year. Others hardly bloomed at all.

Other things to look at is light and moisture. Some plants can handle changes better than others.