Shedding of leaves in winter normal, otherwise it is having a problem. Would be better off in ground than sitting out of ground in pot, there may have been some freezing and death of roots that year.

Down here these are hardy against hot walls most winters. 1990 winter did appear to take some out. It was the coldest winter in 30 years.

They are marginally hardy in this region. You don't say where in BC you are and it's a huge province with drastic differences in winters - Victoria? Salt Spring Island? Bella Coola?? or Vancouver?

Part of the problem with subtropical plants in this region is lack of summer heat to allow them to grow enough to survive the winter. Victoria/Vancouver area is rather mild in winter, more so than Olympia actually, but still borderline, and it was a very cool summer.

Another part of the problem is shifting plants from inside to outside. Growing conditions are very different - dark and dry inside, bright and damp outside. Most plants don't take well to dark and dry which is why good houseplants are so few in number. The leaves the plants grow while inside won't necessarily be able to adapt to the brighter conditions outside. So, the plant drops the leaves when moved, and grows new ones.

Hopefully your conservatory is very bright. I used to have an unheated sunroom in which I kept potted citrus. They went outside for the summer, but I was very careful to move them when temperatures were similar outside and inside, and the sunroom got plenty of light, facing south and west. Still, they often decided to drop their old leaves and grow a whole new set when moved.

Potted plants can be left outside in winter, but the roots are exposed to freezing temperatures, so it's best to shelter the pot somehow. There are extruded foam pots that insulate the roots while looking like fancy molded terra cotta. I sink my bonsai plants into potato crates filled with wood shavings to insulate the roots.

Pomegranites are subtropical. In warm-winter areas like Northern California, they stay evergreen, but not every winter - if there's a hard frost they drop their leaves and grow new ones. It's a normal response to freezing temps for this subtropical plant, but it does slow down their growth the next spring. I'm not sure why your pom would be losing its leaves now. There has been nothing even close to frost yet here in the Puget Sound area, but again I don't know where you are - had frost yet? or a sudden drop in temps?

If it's always been left outside you might want to continue to leave it outside, with some kind of shelter for the roots. Moving back and forth does stress the plant.