SwiftUI NSManagedObject changes do not update the view - swift

Question

In my view model, if I update an NSManagedObject property, then the view won't update anymore. I have attached the code and the view model.
I added a comment in front of the line that breaks the view update.
class StudySessionCounterViewModel: ObservableObject {
fileprivate var studySession: StudySession
init(_ studySession: StudySession) {
self.studySession = studySession
}
#Published var elapsedTime = 14 * 60
#Published var circleProgress: Double = 0
var timer: Timer?
var formattedTime: String {
get {
let timeToFormat = (Int(studySession.studyTime) * 60) - elapsedTime
let minutes = timeToFormat / 60 % 60
let seconds = timeToFormat % 60
return String(format:"%02i:%02i", minutes, seconds)
}
}
func startTimer() {
self.timer = Timer.scheduledTimer(timeInterval: 1, target: self, selector: #selector(self.timerTicked), userInfo: nil, repeats: true)
studySession.isActive = true //Adding this stops my view from updating
}
#objc func timerTicked() {
elapsedTime += 1
circleProgress = (Double(elapsedTime) / Double(studySession.studyTime * 60))
}
func stop() {
timer?.invalidate()
}
}
This is the view that uses that view model. When adding that line, the text that represents the formatted time no longer changes and the progress circle's progress remain the same.
If I remove the line, everything updates and work as expected.
struct StudySessionCounterView: View {
#Environment(\.presentationMode) var presentationMode
#ObservedObject var studySessionCounterVM: StudySessionCounterViewModel
var studySession: StudySession
init(_ studySession: StudySession) {
studySessionCounterVM = StudySessionCounterViewModel(studySession)
self.studySession = studySession
}
#State var showAlert = false
#State var isCounting = false
var body: some View {
VStack {
ZStack {
Text(studySessionCounterVM.formattedTime)
.font(.largeTitle)
ProgressRingView(size: .large, progress: $studySessionCounterVM.circleProgress)
}
Spacer()
if isCounting {
Button(action: {
self.studySessionCounterVM.stop()
self.isCounting = false
}) {
Image(systemName: "stop.circle")
.resizable()
.frame(width: 64, height: 64, alignment: .center)
.foregroundColor(.orange)
}
} else {
Button(action: {
self.studySessionCounterVM.startTimer()
self.isCounting = true
}) {
Image(systemName: "play.circle")
.resizable()
.frame(width: 64, height: 64, alignment: .center)
.foregroundColor(.orange)
}
}
}.padding()
.navigationBarTitle("Matematica", displayMode: .inline)
}
}
UPDATE: Found out that each time the NSManagedObject changes a property, the view model gets reinitialised. Still no solution, unfortunately