My experience is that it takes a while to adjust. I added Hygro 'angustifolia' and Hygro corymbosa to my tank on the same day about 2 weeks ago. The 'angustifolia' has recently started growing at a much faster pace than the corymbosa.
I've only had the 'angustifolia' (and only for a month now). It started growing very fast from the day I put it in the tank and has never stopped. I've trimmed 3 times already. I don't do anything special, just tap water (hard water), EI dosing, DIY CO2, moderate-high light.
Yep, it's a monster. There's a variety called 'aroma' that Tropica sells (still?) that's HUGE. Leaves 20 inches long and stems as big around as your thumb. I couldn't cut it with regular trimming scissors.
Interesting, mine's been adjusting for a while now in the high tech tank, even killed some in a less 'techy' tank but still a nice amount of light and healthy plants galore. Maybe it succumbs easily to travel shock.
Over the week it's progressed a few nodes with some nice new leaves, seems it was asking me for potassium. Stems are still thin and haven't lengthened noticeably, hopefully it'll blow up soon, I was going to move it to mid-ground if it ended up slower than expected.
It also grows very easily emersed. I have it in several tanks in my shop growing over a foot taller than the tanks they are in. The cuttings seem to take root in the water much quicker when the tops are growing above water. In fact they take root all up and down the stems. It makes transplanting them much easier when rooted, and in my experience they don't need to acclimate to being totally submersed either. They just immediately start growing when they are already rooted. I love angustifolia.
I agree with what the others have said. I've had to remove it from my high light co2 tanks because it's too much work. I have it in a few of my lower light non co2 tanks and it is more manageable. Like most hygros, it is a good indicator of any deficiencies you may have. I agree with Robert, I do love this plant but only in my lower tech tanks.