Sanctum Duplicate Boon + Unique Relic not always working as expected

Today the following happened four times already:

I have the sanctum strategy where you stack +2 merchant choices with the unique chalice relic to duplicate divine orbs twice. Most of the times it works as I expect it to: 2 divines go up to 8 and 1 divine goes up to 4.

But sometimes I get less divines than expected, especially when I have more than two rewards at the end of the Sanctum. Once I duplicated 2 divines twice (to 8) and picked another divine reward which should have been 10 in total. But I only got 9. And once I picked a 1 divine reward on floor 4 which should have been 4 divines in the end, but only got 3.

Just now I got really lucky and had the following happen:
I picked up the following three reward rooms in floor 4:
2 divines, 1 divine, 1 divine.
Afterwards I got a shop with the minor duplicate boon AND the major duplicate boon. I picked the major boon first, so > 4 divines, 2 divines, 2 divines
Aftwards I picked the minor boom which duplicated one divine, so > 4 divines, 3 divines, 2 divines.

I did not pick any other rewards. I expected another duplicate of all divines, which would be > 8 divines, 6 divines, 4 divines (18 in total).

I expected to get 18, but only got 15. Do I misunderstand something or is this a known bug. I can post a video of it happening if neccessary.

bug still appearing

It appears you've encountered an unusual issue with the Sanctum Duplicate Boon and Unique Relic in the game. This might be a bug, so sharing a video for clarification is a good idea.