So yes it seem splitting 2.5k GUF2s is now pretty much refused in all cases. There have been reports of this over the last few months, so definitely not a one off refusal.

Not to try and be repetitive, but GUFs at 7k and above (if you choose them vs a joker or 50k avios) are given by default as 2x Guf1s. There is no splitting required.