I remember seeing a comment about this somewhere before, thinking it was nonsense and going on about my day. But it stuck in my head and when I tried to look for the comment, I couldn't find it.
I also couldn't find anything in the game that suggested that infra now also boosts infra. Could you give us more information about what you're seeing?
Just as a random example, when I go to build infrastructure starting up a new game as Turkey, you get the following modifiers:
Factory Ouput: 5.00
Construction Speed: 46.20
Output From 6 factories: 30.00
Construction Speed modified by:
Export Focus: +10.00%
State Infrastructure: x1.40
I never use mods or anything, and the math checks out if that listed construction speed is accurate (30x1.1x1.4). I think it might effect its own build speed now unless something really odd is happening. Ive tried this with multiple countries too.