Yes, I noticed this last night too. What was worse, I didn´t get any gains either. The char is at 20 in stealth skill, has decent hiding, skill meter pointing upward and is not near her overall cap. Haven´t played the char for 3 weeks, so she should be getting quite a few gains. But, nada. Will log in later to see if things have improved today, otherwise I´ll fill in a bug report.
What the character's wearing has some bearing on the gains.
I'm not sure there's a concrete formula known, though. Most of the theories I've read have been observations, which are subject to interpretation.
At around that skill, though, you'll want to be wearing next-to-nothing.
It's possible that even clothes can affect it.
If you train it in a house, then you'll have guaranteed success on your hiding checks, which would at least minimize the time waiting for a successful hide.
If you're on a production shard, then take a wander to New Haven, and you can buy up your skill to 40, at which point I think you can get reasonable gains from a few pieces of leather armour.
If you're on Siege, you might want to beg some +stealth jewellery, to raise your skill a little. sometimes gains are incredibly odd at low skill.
