I've been checking this thread, daily, as I went through all this just one year ago.
It's horrendous, what they out you through.
Your Local Authority have already accepted that you meet their criteria, and that they have an obligation towards you.
Housing Associations will have tenants with less than perfect credit stores. It's why they exist, ffs! After all, if you had a perfect credit score and no money worries, you would just rent somewhere lovely, of your choice, or get a mortgage, wouldn't you?
It took mine 7 months from the offer until moving in. Partly, because of the difficulty of providing all the required evidence, electronically, during lockdown. So, hopefully, the face to face at head office is a good thing. You've advocated well for yourself, so far, but is it worth having someone with you at the meeting? Someone 'professional'?
My son had excitedly told his teachers that we were moving, so they kept asking at drop off/pick up, how the move was going. When it became clear it wasn't happening, they offered support. The pastoral care woman (sorry, I don't know her official job title) offered to support me. In the end, the Head got involved, as they were so shocked by the inefficiency of the HA. I was reluctant, at first, because I'm used to being independent and didn't want my son to be 'judged' but I definitely think that their involvement helped.
I have all my ✌for you.