Pulling out of my sale?

Hi. Long story short. I accepted an offer early Jan. Buyers solicitor has been useless and the buyer seems super passive and is just leaving his solicitor to it. They waited about 6 weeks before raising any queries. I sorted everything they came back with within about 2 days. For the last 5 weeks or so the buyer has just been saying he's waiting to hear back from his lender after getting the fire risk assessment and the lease details clarified.

I've never known a lender take more than a few days (maybe a week) to confirm if they can lend. I feel like he's hiding something. Around mid March he said he would like to complete beginning of April. A week later he changed his mind and said to complete end of April. I've been pushing to get exchanged so at least it's locked in but they just keep saying they're waiting on the lender. My EA has said him and his solicitor have been extremely hard to get hold of. They can't get any solid details about what the delay is and why it's taking so long. My solicitor is just stuck and says there's literally nothing more to be done (as has been the case for multiple weeks now).

I just feel like something is wrong and he is stalling for some reason. I'm leaning towards asking for the property to go back on the market to see if it sparks a bit of urgency from his side to get things sorted. He has no chain and neither do I.

Would you just stick with it and hope he pulls his finger out or get it back on the market as it feels like he's a bit of a time waster to be honest!