Just recruited him again, and he counts like a new character, with no portrait and 25 ability score points to spend (but his starting stats aren't 10 - they're his "real" stats, so I can potentially start him with 30 dex for example).
Loading an earlier save and recruiting him again yields the same result.
Any ideas?

Are you running any mods on that?

Update: Reloading the same file 10 times didn't help (not that I thought it would), and neither did levelling up all the other current companions (Wenduag, Seelah, Camellia) before recruiting him.
What did apparently help loading the game and then going out on to the city map and then back again and recruit/free him. He now has his proper level and stats.

That seems interesting. Seems there are still issues around respec a character which even transfers to recruiting. Seems the patch which is supposed to save the game from the critical issue needs further improvement.

Make sure to report it via the ingame tool (ALT+B).

when you are in the abbys you and choose the path for woljif
you need to retrain him at the flash market

this game have some major issues when it comes to retraining etc

this is after he flees during the garg attack?

Far, far after when he ran away. Probably when you reach that point there will be a new patch available already.

yea FAR away in Act V (so they say) you know when you visit that nice place that's always nice breech of hot air.

no after the garg attack i don't think he have much trouble after act V.

and yes this game have a lot of trouble with retraining it comes do to the quest toggles after you toggled a certain quest you can't untoggle it (without a mod)

the devs should limit the retraining to paths so the game is lot more stable.