In testComplete 12.1, the following bugs reported by our customers have been fixed:

Improved QuerySelectorAll performance in Edge and Chrome.
Fixed: Object coordinates in Edge were calculated incorrectly if the Favorites bar was displayed.

Note: Users need to restart Edge after adding or hiding any toolbars to avoid the issue in the future.
Fixed: TestComplete could not identify JavaScript dialogs (such as Alert) in Chrome on Windows 10.
Fixed: The Firefox crash when using the Highlight on Screen command in TestComplete.
Fixed: The Finder tool could not identify web page elements in Firefox in some multi-monitor environments.
Fixed: In Internet Explorer, the FindChildByXPath method sometimes returned a native DOM object instead of a TestComplete wrapper for this object.
Fixed: TestComplete stopped identifying web page elements in CEF applications after a few test runs.

Fixed: Slowness when working with objects identified via the UI Automation engine on Windows 10.
Fixed: TestComplete could not select items in a WPF pop-up menu during the test playback.
Fixed: Incorrect name mapping recorded for some objects in Visual Basic 6 applications.

Fixed: UI rendering issues on VMware 12 virtual machines running Windows 10 with the Accelerate 3D graphics option turned off.
Fixed: Incorrect sorting by the Date column in TestComplete panels.
Fixed: Hanging when opening the Stores | Files editor from the Project Explorer.
Fixed: Errors in the Stores | Regions editor after certain sequences of actions.
Fixed: A spelling error in a message displayed by the License Manager.

Fixed: Missing network suite files after converting a source control-bound project to the TestComplete 12 format.
Fixed: A crash when converting a project stored in Team Foundation Version Control to the TestComplete 12 format.
Fixed: Script files checked out from Team Foundation Version Control were deleted from the hard drive on saving.
Fixed: Hanging when loading a project bound to a large Git repository (>50 GB).

Fixed: Crashes when creating projects and when closing TestComplete.
Fixed: A “Catastrophic failure” error when playing back certain tests if the TestComplete UI layout was customized.
Fixed: Memory leaks when using Code Completion.
Fixed: Memory leaks when editing Python scripts.
Fixed: The slPacker.Pack method did not work in TestComplete 12.
Fixed: Runtime changes to the values of persistent variables were not saved in project files.
Fixed: A missing confirmation prompt when closing a project with unsaved changes to the persistent variables.
Fixed: The SendMail function hanged when attaching a file to an email.
Fixed: A wrong value of Log.FolderErrCount if Log.LockEvents was used.
Fixed: A keyword test playback stopped on a PopupMenu operation even if the Stop on error and Stop on warning options were disabled.
Fixed: The installation program could not detect Visual Studio 2015 Test Agent and install the corresponding integration.
Fixed: Missing step instructions in exported manual tests.

Bug Fixes in TestComplete 12.1