I wouldn’t say it’s unusual to sign another contract when you get here. Were the terms different or was it just the missing signatures? Who knows what happened to the one they gave you/you sent them, but not really important unless they’re blatantly changing things. Chances are it was simply lost or misplaced, but it sounds like there may be other red flags here. I believe they have to give the PSB the signed/counter signed contract when they apply for your visa, so I’d say that’s the bigger question as mentioned above.