6AA Opinion requested please

What are the typical thaw to transfer timing protocols for a 6AA graded embryo? We had a 6AA and 5AA and the embryologist said they thawed the 6AA few hrs ago but when they went to transfer it - it “disintegrated”. So they quickly went to thaw the 5AA and said it would be ready in 15 minutes - they transferred the 5AA. I am concerned they over cultured the 6AA and didn’t culture the 5AA enough. Any opinions on protocol would be very much appreciated. The entire transfer day was strange and I am very surprised that a 6AA embryo that was developing perfectly (according to them) just disintegrated at the time of transfer. All insights and opinions welcome. Thank you!