Why would a seller instruct a valuation after accepting an offer?

I made an asking price offer in late Feb that was accepted. My survey was completed in late March after the chain was completed when I was told the sellers had reserved a new build.

I answered a phone call today from the surveying company apologising that they couldn’t complete my booking due to conflict of interest with my sellers valuation. They didn’t realise at first that my survey had been completed already, but then found it on their system and apologised saying the finance team had made a mistake and it was the sellers that couldn’t have their valuation completed.

I’m now stuck thinking of scenarios of why my sellers may be getting a valuation. All I can think of is that it may be a tool to try to renegotiate the price higher, either by asking me for more or by testing the price of part exchanging against my offer. Can anyone help put my mind at ease by suggesting other reasons for it?