Based on player feedback our recent change to blueprint equip time prediction had some unintended consequences. We're going to deploy a hotfix to change it to how it was before v9.10. We'll continue to work towards improving this.— Fortnite (@FortniteGame) May 23, 2019
Some Fortnite players have noticed a glitch after the game's most recent update that causes their guns to go invisible when quickly swapping between edit and fire modes. It seems Epic is already on-top of this issue, and has deployed a hotfix to revert things to how they were prior to Version 9.10. No need to download any data, as the update is applied server-side.