So back around April time I remember emailing Daniel Vogel as I literally had ALL nodes pertaining to power level in both the skill tree and the research tree (with all maxed survivors) yet my PL was like 124.9. The bar was like a pixel off. As you can imagine this was very frustrating. I learned afterwords that your squad bonus actually counted as single points towards your PL so I had to do a slight rejig and I finally reach the promised land of 125. After I told Daniel my plight (as probably maybe a few others did, I couldn't say) the dev's went ahead and patched it to make it easier in patch 3.6: Fixed an issue where high level players could only hit Power Level 124. They can now get up to Power Level 125.
I knew another guy at the same time who was perpetually stuck at 124.8 or something as he was missing two Fort nodes and he couldn't get anymore skill points (even from the collection book). Thankfully the patch bumped him up and saved him from clawing his face in frustration.
With the patch it doesn't matter anymore but I would highly advise not doing the nodes in order as you will increase your wait time by quite a bit.