Rock Band 4 publisher Mad Catz has apologised for a shortage of Xbox One edition stock.
Specifically, customers are having difficulty purchasing the physical version of the game with the Legacy Game Controller Adapter, which allows Xbox 360 instruments to be used via Xbox One.
Amazon, Game, GameStop and ShopTo are all currently showing the item as "out of stock" at the time of writing.
Eurogamer readers have also received emails from Amazon stating that the company is "still trying to obtain" the product - with orders delayed until further notice.
The digital edition of Rock Band 4 is also available to download via the Xbox One Games Store, although you will need new Xbox One-compatible instruments to play the game - or the adapter to use Xbox 360 instrument models.
PlayStation 3 instruments are supported as standard with no adapter required, which is probably why there is no similar shortage for the game's PS4 edition.
"We're thrilled at the reception both critically and commercially to Rock Band 4 and have been overwhelmed with demand since pre orders opened," Mad Catz global PR exec Alex Verrey told Eurogamer.
"For months now we have been saying again and again how important it was to pre-order if you wanted to receive hardware on day one. We did warn that demand would be high!
"To reassure fans, the standalone version of the game on Xbox One (which comes with the Legacy Game Controller Adapter included) has absolutely NOT been delayed in any way. As promised, it is shipping today and those who pre ordered will start receiving it from today.
"Retail will also be stocking it from today, with the game on shelves nationwide, however, as stated earlier, demand is high. More stock will be arriving throughout October and I would like to stress that the quickest way to ensure delivery is to get an order in now via retailers such as Game, Amazon or indeed the Mad Catz website.
"We're deeply sorry if any fans are having difficulty purchasing today, we're doing everything we can to make sure more stock arrives very shortly."