I've not heard that before. the RHS doesn't mention it either.
here is the link to it.

https://www.rhs.org.uk/Plants/90456/Crinum-x-powellii/Details

Hi, Crinum x powellii is fully hardy, and needs a deep, fertile, humus rich, moist but well drained soil, in full sun, so the position it's in could be, 1, not deep enough fertile soil, 2, too dry as it is right up to the wall, I would suggest preparing a new planting spot, adding loads of humus to the planting area, away from the wall, and if the ground is very dry, it will need plenty watering in the growing season,this should improve flowering, if this is the height it gets to each year, it only appears to be about half the height it should get to, which is about 5ft, Derek.

I tried some Crinums in pots, and they didn't like it. So last year I moved them into the ground, and they have multiplied, but not flowered. They really don't like to be moved or divided. The Crinum moorei's that I have only give 1 stalk per bulb, and in the 30 years that they have been there (actually more because they were there when I bought my land) they haven't really multiplied that much. New clumps from seed, but limited offsets.

I think i did put it in the wrong place there you go.....May just move it away from the wall as no where else to put it. Many plants require moist soil and sunshine a difficult feat in most suburban gardens

Hi, yes it's an almost impossible situation in most gardens, unfortunately a lot of plants insist on it, others don't mind too much, as long as their roots aren't waterlogged, Derek.

I remember now that Bob flowerdew back in 2013 recommend that these were not hardy and needed to be in a container to brought inside in the winter that's what would have led me to it it in a sunny position up against the wall on the first place

Hi, when you move it away from the wall, make sure you put plenty of humus material in the hole, and also mix in with the soil you take out and back fill with, and keep it well watered until it establishes itself again, Derek.