Same issue, impossible to launch a session and work on my island 
Get 4 error logs.
3 of them report that a definition is more accessible than its dependencies, even though everything was working fine before the update.
C:/Users/Shadow/Documents/uefn-roguelike-project/UefnProject/Plugins/MainGame/sys/published/Content/Game/Scripts/Heros/damage_display.verse(32,5, 32,84) : Script error 3593: Definition (/loomio@fortnite.com/roguelikeproject/Game/Scripts/Heros/damage_display:)DigitMaterials is accessible from subtypes of damage_display, from subpaths of /loomio@fortnite.com/roguelikeproject, but depends on (/loomio@fortnite.com/roguelikeproject/Game/Materials:)DamageDigit_Opti_material, which is only accessible from subpaths of /loomio@fortnite.com/roguelikeproject/Game/Materials, /loomio@fortnite.com/roguelikeproject. The definition should be no more accessible than its dependencies.
C:/Users/Shadow/Documents/uefn-roguelike-project/UefnProject/Plugins/MainGame/sys/published/Content/Game/Scripts/Heros/damage_display.verse(32,5, 32,84) : Script error 3593: Definition (/loomio@fortnite.com/roguelikeproject/Game/Scripts/Heros/damage_display:)DigitMaterials is accessible from subtypes of damage_display, from subpaths of /loomio@fortnite.com/roguelikeproject, but depends on (/loomio@fortnite.com/roguelikeproject/Game/Materials:)DamageDigit_Opti_material, which is only accessible from subpaths of /loomio@fortnite.com/roguelikeproject/Game/Materials, /loomio@fortnite.com/roguelikeproject. The definition should be no more accessible than its dependencies.
C:/Users/Shadow/Documents/uefn-roguelike-project/UefnProject/Plugins/MainGame/sys/published/Content/Loomio/Text3D.verse(85,9, 85,107) : Script error 3593: Definition (/loomio@fortnite.com/roguelikeproject/Loomio/Text3D/char_prop:)Material is accessible from subpaths of /loomio@fortnite.com/roguelikeproject, but depends on (/loomio@fortnite.com/roguelikeproject/Game/Fonts:)NotoSans_Material_material, which is only accessible from subpaths of /loomio@fortnite.com/roguelikeproject/Game/Fonts, /loomio@fortnite.com/roguelikeproject. The definition should be no more accessible than its dependencies.
The 4th log is about a missing definition, but that’s expected. The class was removed from the game last week. There were no issues related to this before the update.
C:/Users/Shadow/Documents/uefn-roguelike-project/UefnProject/Plugins/MainGame/Content/Game/ModuleDefinitions.verse(34,26, 35,1) : Script error 3643: Missing definition in source package that corresponds to published definition (/loomio@fortnite.com/roguelikeproject/Game/Scripts/UiDefinitions/Menus:)card_types.