After some digging I found out that SwiftData is causing the problem. More concrete relationships I have a class Account with has (optional) categories @Relationship(deleteRule: .cascade, inverse: \Category.account) var _categories: [Category]? var categories: [Category] { self._categories ?? [] } in the class Category I have the a simple account variable var account: Account The application crahses when I use the following init function in Account (at the last line) init(id: Int, income: Bool, location: String, maintainance: Bool, special: Bool, taxRate: Float, tenant: String, title: String) { self.id = id self.income = income self.location = location self.maintainance = maintainance self.special = special self.taxRate = taxRate self.tenant = tenant self.title = title self._categories = [] } or when I use those lines // category not found, so create one let category: Category = Category(title: categoryName, account: self) if self._categories == nil { self._categories = [category] }