Hunters beware - Capcom has discovered a bug in Monster Hunter: Rise which could result in players losing certain materials under specific circumstances. This bug is apparently an issue in all versions of the game, including on Nintendo Switch.
The bug occurs if players choose the “Create Decorations” or “Forge/Upgrade Weapons/Armor” options at the Smithy, select one or more material types/armor spheres, then cancel, then proceed to create a decoration. Taking these steps in this exact order could result in those materials or spheres disappearing completely.
Capcom is currently working on finding a solution to the issue. In the meantime, if this happens to you, Capcom recommends restarting your game without saving. See below for their official statement.