One leaf on Cattleya bulb
 

I bought this "Slc. Little Hazel 'Red Jewel'" at a local nursery a few months back, and it had a small growth. It has now matured, but the new pseudobulb only has one leaf, rather than two leaves like the old growths. Is this something to be worried about? I've heard that some hybrids have an unstable growth pattern, but I'm not sure that is the case here.

Not to worry. This plant had both bifoliate and monofoliate parents so it can grow a growth with either and it's not a problem. If the growth is healthy and hopefully larger than the previous growths then you are doing fine.

When the plant is fully mature it will probably settle onto one type of another but young plants can be all over the place.

P.s. it may or may not be helpful to know but your plant is now classified as (Ctt.) Cattlianthe Little Hazel 'Red Jewel'