My advice is not to take all this advice here too seriously. Each problem will have 5 solutions on any given post (and some advice will conflict).
Something is wrong. You should not have pH that high in brand new soil. Usually, it takes a few weeks for the pH to rise that much. I have a hard time believing that "just adding nitrogen" is going to fix everything. I suspect if you continue adding stuff, you'll make it worse. I could be wrong though. Every situation is different.
Before more steps, I would get a PPM meter and test the run-off water. If it's over 400ppm then I would not add nutes at this point. If your pH didn't come down to at least 6.5 then you didn't flush enough.
As for what happened, I'm guessing shock. Coco to hot soil is a big change. I did that once with a seedling. It stopped growing for about 1 month!!! It didn't die but didn't grow. The soil stayed super wet, and I put the plant back in the corner, assuming I killed it. After about 4 weeks, it exploded with growth. I did nothing - no water even. Eventually, I repotted in 5G and it did great.
What I've been learning (the hard way) is that soil is everything. Mix the soil with some coco to dilute it maybe? I've also had much better growing success amending my used soil with Earth Base and Earth Dust, then I reuse it as new. This seems to make the plants happier for longer. Allegedly, the used soil will "mature" over time and become better and better. I'm only on maybe the 3rd grow using the same soil, so I'm not sure yet. So far, so good.