I had a day lily that had the same problem for several years, 'Cezanne'. The flowers were large but on 6" scapes so basicly on the ground. I tried making sure it got routine fertilizing & treatment like others in that day lily bed but nothing changed. All left to try was moving it to another day lily bed. I moved it & it started getting normal scapes the next bloom cycle. I'll never know what it was but a couple of years now & it has 12" to 15" scapes. That's still shorter than they should be but time may balance it out. Give that a try if possible.
