Edit 1: Those issues have also been reported on the EU Forums. The problems have arise after Pre-patch, during the Shadowlands launch.
With the squish, new zones and items became accessible to characters of all levels. Due to the great scale of the project, naturally some things didn’t go so smoothly.
Some items seem to maintain hidden level requirements that don’t show in their tooltips, despite being acquirable for characters of much lower levels. Those items are very variable in nature, being recipes, lockboxes and etc.
An intended fix is to either remove the internal requirements or reflect the restrictions in the tooltip, to display clear information.
Below I will list some of the items that I came across (the list may be increased over time!).
• Ghost Iron Lockbox - Can’t be opened by a character of at least level 20, even when unlocked.
Error: “Your level is too low to use that item”
• Small Iron Metamorphosis Geode & Large Iron Metamorphosis Geode - Show red in the vendor for a level 20 but are purchasable. Can’t be open, despite not showing level requirements in-game.
• Schematic: Jeeves - Can be obtained by a level 20, but simply can’t be learned even at the respective 75 profession skill.
• Large garrison blueprints bought with Comprehensive Outpost Construction Guide can’t be used by a level 20, despite the Talador questline being available.
• Nitro Boots Tinker - Cannot be applied to belts of an item level inferior to 30, despite not requirements being made on the tooltip.
• A not fully comprehended number of Enchantments and Recipes seem to require a hidden character level to work and/or be applied.
Apparently this is more common with Battle for Azeroth enchants such as Accord of Haste.