This creeper just spawned in the doorway, which should have enough light to not makes mobs spawn.

Recently, after the nether update which apparently changed mob spawning, my friend and I have been encountering problems with lighting. My friend and I were building a theatre in survival mode. On a world from earlier this year, we also built a theatre in survival, and for the seating, we lit it up with Redstone torches as we didn't want a lot of light there during the performance. This time, when we lit up every part of the seats with Redstone torches, mobs still could spawn. It was like the redstone torches didn't affect the lighting at all. Then, we decided to put regular torches underneath each stair block, however in the three blocks of space between the stage and seats, there was a little area of shadow, somehow this was enough room for mobs to spawn, even though it was not that dark. There is an upstairs area which we have lit up with torches yet still seems to spawn a lot of mobs. I will attach pictures of both areas I just described. I understamd that mob spawning needed to be fixed, but it feels like mobs just disregard any light, or spawn in an area if it has just the tiniest bit of darkness.