[nemesis-]

Use SetSpawnInfo (https://sampwiki.blast.hk/wiki/SetSpawnInfo) instead of that bit of code you're using inside OnPlayerSpawn. It is far more reliable and doesn't require the frequent resetting of the player's skin like you're trying to do in OnPlayerSpawn. I encountered similar oddities long ago and ended up resorting to this.

Your Dcmd for vskin looks logically and syntactically correct though, remember, anytime someone changes their skin using that command, you have to reset their SetSpawnInfo settings or they will spawn using the old skin.

EDIT: Also, don't use it onplayerspawn, use it inside onplayerrequestskin and the skin command.