Thanks for the info. This is caused by CS2 inventories that have items, but which have no items that are actually visible. The returned data looks like garbage because Valve.
steamcommunity 3.48.5 fixes the error, instead returning an empty array.
As of steam-tradeoffer-manager 2.11.7, you can use the deprecated TradeOffer.loadPartnerInventory() method to get those CS2 items.