I had two expiring 241 vouchers. A while.back I did the ",book and cancel" routine to get the vouchers extended. They were duly extended to Sept 2023.

Likewise, I cannot see them on mobile app. Nothing showing at all under "my vouchers" etc. They just disappeared some time back. However on the desk top after seeing the Op original post, I have found them with indeed numbers associated to them. I have not yet tried to use them as I agree I don't see where you can! Also did BA not get "wind" of the buying and cancelling to get vouchers existing but expiring vouchers extended and then decided just to give the tax paid money back hence losing the voucher? I can't recall. It's all a bit odd.