UIProgressBar within CollectionViewCell always set to 1.0 after being in background

Question

I'm stuck while working on a custom calendar. Each day is within an Array and then put into custom CollectionViewCells.

Within the cell of the current day, I want to put a kind of "marker" (I use a UIProgressBar for this) to show the progress of the day. Means at noon of today, the UIProgressBar should be at 0.5 and so on.

To handle this, I have the following function which return a Float with one decimal to use it in the UIProgressBar:

    func getPercentage() -> Float {

        var cal = Calendar(identifier: .gregorian)
        cal.timeZone = TimeZone(abbreviation: "UTC")!
        let hours = cal.component(.hour, from: Date())
        let minutes = cal.component(.minute, from: Date())

        let allHours = Float(hours) + (Float(minutes) / 60)
        
        let result = round((allTimeInHours / 24) * 10) / 10
        
        return allTimeInPercent
    }

Within the cellForItemAt indexPath im checking if the cell is the cell of today, and if it's the case, I'm calling the getPercentage() method to set the UIProgressBar within the cell accordingly:

    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: MyCollectionViewCell.identifier, for: indexPath) as! MyCollectionViewCell
        



    //other functionality + cell-setup
 
        
        if dateArray[indexPath.item] == todayAsDate() {

            cell.progressBar.isHidden = false
            cell.progressBar.progress = getPercentageOfDay()

        } else {

            cell.progressBar.isHidden = true
        }
        
        return cell
    }

So far everything works fine and looks like this:

However whenever I go to the Home Screen and then back to the app, the UIProgressBar is always set to 1.0.

After completely closing out the app via the AppSwitcher and restart the app, everything works fine again.

Im guessing there's a problem because I use dequeueReusableCells but im not really getting behind it. I don't know where the 1.0 for the UIProgressBar is coming from, even when I change the default in the Storyboard the result is the same.

Also if anyone has a suggestion to use something else than a UIProgressBar im open for any ideas. Actually I would prefer to just have vertical line moving left to right according to the time of the day.

I'm pretty much a beginner and happy for any hints! :)