I play on Xbox 360. Since I met Alduin for the first time, I have killed two dragons and they did not incinerate like the others, but just died. No soul to collect. Is this a known bug or do I have to complete a quest to start absorbing souls again ?

Thanks for all the answers.

Is this a dragon at a word wall that respawned after you killed it before?
Because those dragons will not give a soul apart from the first time you kill them.

Thanks, Merari. This is exactly what happened ! Problem solved.

Glad I could help

I've been able to absorb their souls the second time..

Oh, so that's why! Whew! For a second there, I thought I was boned (assuming a soul for every word).

Even better news: bones, scales, and gold galore.

Here, kitty kitty kitty... *readies bow

Don't they have pills for that? Performance issues arn't all that uncommon in older Dovahkiins.

I hope it hasn't affected any of your relationships in game.