The bug

After growing into a 2 × 2 spruce tree, the generated leaves and logs don't interact with redstone components or update surrounding blocks.

This behaviour is exclusive to 2 × 2 spruce trees. Every type of 1 × 1 tree and 2 × 2 jungle and dark oak trees are updated correctly.

Note: This cannot be tested with observers because they are not only activated by block updates and therefor recognize this changed.

Code analysis

Based on 1.11.2 decompiled using MCP 9.35 rc1

The method net.minecraft.block.BlockSapling.generateTree(World, BlockPos, IBlockState, Random) calls the constructor of the large spruce tree generator with false as value for notify.