I was consequently closing opened code editor tabs with mouse by pressing the X button. Cannot reproduce.

Process: Qt Creator [19305]
Path: /Applications/Qt Creator.app/Contents/MacOS/Qt Creator
Identifier: org.qt-project.qtcreator
Version: 4.12.0 (4.12.0)
Code Type: X86-64 (Native)
Parent Process: ??? [1]
Responsible: Qt Creator [19305]
User ID: 501

Date/Time: 2020-05-01 16:33:26.257 +0200
OS Version: Mac OS X 10.15.4 (19E287)
Report Version: 12
Bridge OS Version: 4.4 (17P4281)
Anonymous UUID: D8B5C5E0-882E-73A8-97AA-8ECBBD9D88D2

Sleep/Wake UUID: 7C4AA4F1-398C-4403-B32C-5B22AAF65945

Time Awake Since Boot: 44000 seconds
Time Since Wake: 2800 seconds

System Integrity Protection: enabled

Crashed Thread: 0 Dispatch queue: com.apple.main-thread

Exception Type: EXC_BAD_ACCESS (SIGSEGV)
Exception Codes: KERN_INVALID_ADDRESS at 0x000016d5f1a7ada8
Exception Note: EXC_CORPSE_NOTIFY

Termination Signal: Segmentation fault: 11
Termination Reason: Namespace SIGNAL, Code 0xb
Terminating Process: exc handler [19305]

VM Regions Near 0x16d5f1a7ada8:
mapped file 000000012d42e000-000000012d63c000 [ 2104K] r--/rwx SM=COW 
-->
MALLOC_NANO 0000600000000000-0000600008000000 [128.0M] rw-/rwx SM=ALI

Thread 0 Crashed:: Dispatch queue: com.apple.main-thread
0 libDiffEditor.dylib 0x000000010acf2b0a DiffEditor::Internal::DiffEditorPluginPrivate::updateDiffOpenFilesAction() + 90
1 org.qt-project.QtCore 0x000000010530da95 0x1050e5000 + 2263701
2 libCore.dylib 0x0000000108e23507 Core::EditorManager::editorsClosed(QList<Core::IEditor*>) + 55
3 libCore.dylib 0x0000000108ce2e36 Core::Internal::EditorManagerPrivate::closeEditors(QList<Core::IEditor*> const&, Core::Internal::EditorManagerPrivate::CloseFlag) + 3078
4 libCore.dylib 0x0000000108ce70ad Core::EditorManager::closeDocuments(QList<Core::IDocument*> const&, bool) + 45
5 libCore.dylib 0x0000000108ce21ad Core::EditorManager::closeDocument(Core::IDocument*, bool) + 61
6 libCore.dylib 0x0000000108ce1df8 Core::Internal::EditorManagerPrivate::closeEditorOrDocument(Core::IEditor*) + 152
7 org.qt-project.QtCore 0x000000010530da95 0x1050e5000 + 2263701
8 org.qt-project.QtCore 0x0000000105305cff QObject::event(QEvent*) + 943
9 org.qt-project.QtWidgets 0x00000001043fda3a QWidget::event(QEvent*) + 4698
10 org.qt-project.QtWidgets 0x00000001043c1f5a QApplicationPrivate::notify_helper(QObject*, QEvent*) + 266
11 org.qt-project.QtWidgets 0x00000001043c33e6 QApplication::notify(QObject*, QEvent*) + 598
12 org.qt-project.QtCore 0x00000001052da9f4 QCoreApplication::notifyInternal2(QObject*, QEvent*) + 212
13 org.qt-project.QtCore 0x00000001052dbbe9 QCoreApplicationPrivate::sendPostedEvents(QObject*, int, QThreadData*) + 809
14 libqcocoa.dylib 0x00000001077ab0e9 0x107772000 + 233705
15 libqcocoa.dylib 0x00000001077ab858 0x107772000 + 235608
16 com.apple.CoreFoundation 0x00007fff320c9f12 _CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE0_PERFORM_FUNCTION_ + 17
17 com.apple.CoreFoundation 0x00007fff320c9eb1 __CFRunLoopDoSource0 + 103
18 com.apple.CoreFoundation 0x00007fff320c9ccb __CFRunLoopDoSources0 + 209
19 com.apple.CoreFoundation 0x00007fff320c89fa __CFRunLoopRun + 927
20 com.apple.CoreFoundation 0x00007fff320c7ffe CFRunLoopRunSpecific + 462
21 com.apple.HIToolbox 0x00007fff30cfbabd RunCurrentEventLoopInMode + 292
22 com.apple.HIToolbox 0x00007fff30cfb7d5 ReceiveNextEventCommon + 584
23 com.apple.HIToolbox 0x00007fff30cfb579 _BlockUntilNextEventMatchingListInModeWithFilter + 64
24 com.apple.AppKit 0x00007fff2f346c99 _DPSNextEvent + 883
25 com.apple.AppKit 0x00007fff2f3454e0 -[NSApplication(NSEvent) _nextEventMatchingEventMask:untilDate:inMode:dequeue:] + 1352
26 com.apple.AppKit 0x00007fff2f3371ee -[NSApplication run] + 658
27 libqcocoa.dylib 0x00000001077aa5d3 0x107772000 + 230867
28 org.qt-project.QtCore 0x00000001052d6a7f QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) + 431
29 org.qt-project.QtCore 0x00000001052db002 QCoreApplication::exec() + 130
30 org.qt-project.qtcreator 0x000000010405c967 main + 15143
31 libdyld.dylib 0x00007fff6c010cc9 start + 1

Thread 1:: com.apple.CFSocket.private
0 libsystem_kernel.dylib 0x00007fff6c15a0fe __select + 10
1 com.apple.CoreFoundation 0x00007fff320f2e13 __CFSocketManager + 641
2 libsystem_pthread.dylib 0x00007fff6c215109 _pthread_start + 148
3 libsystem_pthread.dylib 0x00007fff6c210b8b thread_start + 15
....