Hi, thanks for sharing this issue.
The default list of engine modes places 'Run all tests manually' as engine mode 2. This suggests that your list of engine modes has changed from the default.
Check that the 'Run all tests manually' engine mode underneath the Custom Engine Modes dialog. The Automatic Test Filter for this engine mode should be set to 'False' with no other conditions. If you're unsure about this, the easiest way to confirm the correct arrangement is to shut down and re-open the IDE with no projects open, then create a new empty solution. The engine modes will then be populated with the defaults.