Meanwhile I complained to e-rewards about the non-availability of Avios redemption on my account. Here's their useless answer.

While we are tweaking a few things to optimize the brand-new website, some reward options may not be available for redemption straight away.

Don't worry, this is just temporary. Do keep an eye on your account rewards section, as all your favourite reward partners will gradually be made available again.

Thank you for your patience and understanding.