I'm in a similar position to you @areyouhavingagiraffe. I was on the threads last summer as well with my previous purchase which collapsed after my elderly vendor pulled out after 7 months.
I'm now in a chain where there's me, my vendor, and their vendor, who is renting out the house my vendor is buying. It's the tenant who isn't ready to move out, which suggests the vendor didn't give them notice until very recently.
I've been ready to exchange since June, and have gently tried to encourage my vendors to break the chain by moving in with family, but they don't want to chance it, so are staying put.
My mortgage offer runs out in 2 weeks, which everyone has been aware of since May!