welcome to GoY
have a look at this link. lots of info on their care.

https://www.rhs.org.uk/Plants/119869/i-Rosa-rugosa-i-Rubra-(Ru)/Details

It must be in full sun - 6 hours of sun per day.

the rhs site suggests it will manage well in part shade and certainly the one down the road never gets direct sun due to the garage next to it.

'Best flowering and disease resistance generally occur in full sun.' Full Sun = 6 Hrs.

http://www.missouribotanicalgarden.org/PlantFinder/PlantFinderDetails.aspx?taxonid=286364

Pruning it heavily in early spring will cut off all of the flower buds, too, on older varieties.

yes Bathgate but that doesn't mean it wont survive and flower in partial shade. I have several books that support both planting positions. The RHS advice is that it 'tolerates' shade. so perhaps that's why lis is finding it is flower shy after the pruning its had.

maybe try to feed them with balanced feeds (seaweed feed)3 times outside the growing season from winter through out till summer, mulch them and wait for another year, they need condition the soil if not grown for years.