OK, some strains do seem to start flowering with as little as 10 hours darkness outdoors.
If it is this long light cycle that should be keeping it in veg, there are the pre-flowers to think about. But I don’t think this is just pre-flowers.
On many strains these pre-flowers can seem to get pretty prolific, and especially on clones that are kind of old. It might be a genetic thing, and might be from the equatorial strains that naturally themselves could survive a very long time, and even have more than one season outdoors. They’ll get to a certain age and seem to want to stay in an almost perpetual semi-flower, not quite pre-flower and certainly not full flower, and actually maybe flower 2 times a year, during the two separate flowering seasons some of these equatorial areas have. Also seedlings can naturally grow from seed to flower in these separate seasons.
I seem to have been able to force clones out of this state by making sure the light is not only a long day cycle but longer than the one you are using, more of a 16/8 or even 18/6, even 24/0 if it’s a clone – not a seedling.
Also a decent amount of light intensity is needed. You might want to try bringing the lights a lot closer for this added intensity. This is what you want to do if you are trying to get it to veg longer, and get it to bush out.
With a seedling, I think a longer light period might be needed to also get this plant to veg better, but don’t be surprised if you might get a sex reversal (hermaphrodite flowers), this will have some to do with the genetics of the seed as well, if you are lucky it will be a true female and won’t have a tendency to hermi.
Also stress can be a contribution, as mentioned, but I’m suspecting you mostly need a longer photo period for this strain if you want to maintain veg.