For some time now Xcode has been downloading crash reports from users of my app about crashes related to arrays. One of them looks like this:

...
Code Type:             ARM-64
Parent Process:        launchd [1]
User ID:               501

Date/Time:             2024-07-18 14:59:40.4375 +0800
OS Version:            macOS 15.0 (24A5289h)
...

Crashed Thread:        0

Exception Type:        EXC_BREAKPOINT (SIGTRAP)
Exception Codes:       0x0000000000000001, 0x00000001045048b8

Termination Reason:    Namespace SIGNAL, Code 5 Trace/BPT trap: 5
Terminating Process:   exc handler [1771]


Thread 0 Crashed:
0   MyApp                       0x00000001045048b8 specialized Collection.map<A>(_:) + 596
1   MyApp                       0x00000001045011e4 MyViewController.validateToolbarButtons() + 648 (MyViewController.swift:742)
...

The relevant code looks like this:

class MyViewController {
    func validateToolbarButtons() {
        let indexes = tableView.clickedRow == -1 || tableView.selectedRowIndexes.contains(tableView.clickedRow) ? tableView.selectedRowIndexes : IndexSet(integer: tableView.clickedRow)
        let items = indexes.map({ myArray[$0] })
        ...
    }
}

The second crash looks like this:

...
Code Type:             X86-64 (Native)
Parent Process:        launchd [1]
User ID:               502

Date/Time:             2024-07-15 15:53:35.2229 -0400
OS Version:            macOS 15.0 (24A5289h)
...

Crashed Thread:        0

Exception Type:        EXC_BAD_INSTRUCTION (SIGILL)
Exception Codes:       0x0000000000000001, 0x0000000000000000

Termination Reason:    Namespace SIGNAL, Code 4 Illegal instruction: 4
Terminating Process:   exc handler [13244]


Thread 0 Crashed:
0   libswiftCore.dylib                  0x00007ff812904fc0 _assertionFailure(_:_:flags:) + 288
1   MyApp                               0x0000000101a31e04 specialized _ArrayBuffer._getElementSlowPath(_:) + 516
2   MyApp                               0x00000001019d04eb MyObject.myProperty.setter + 203 (MyObject.swift:706)
3   MyApp                               0x000000010192f66e MyViewController.controlTextDidChange(_:) + 190 (MyViewController.swift:166)
...

And the relevant code looks like this:

class MyObject {
    var myProperty: [MyObject] {
        get {
            ...
        }
        set {
            let items = newValue.map({ $0.id })
            ...
        }
    }
}

What could cause such crashes? Could they be caused by anything other than concurrent access from multiple threads (which I’m quite sure is not the case here, as I only access these arrays from the main thread)?