Description of the Issue

When I open a second (third, fourth) instance of Notepad++ (for example, by click on the "Open in New Instance" tab menu item), and open a Project panel in that new instance then this panel is almost unnoticeable because it is only a few pixels wide.

Steps to Reproduce the Issue

1. Open any document. (Optionally, click on "View" -> "Project panels" -> "Project Panel 1".)
2. Click on the "Open in New Instance" tab menu item.
3. In the new instance click on "View" -> "Project panels" -> "Project Panel 1".
4. Try to find the Project panel.

Expected Behavior

The Project panel in the second instance should have the same width as in the first one.

Actual Behavior

The Project panel in the second instance is only a few pixels wide as screenshots below demonstrate:

The first instance:

The second instance before the Project panel opening:

The second instance with the Project panel opened:

Note a thin gap between a left window border and a left tab border on the last screenshot: this is not the gap, but the Project panel! And it can be expanded by mouse to a normal width!

Debug Information

Notepad++ v7.9.2 (32-bit)
Build time : Dec 31 2020 - 03:58:36
Path : C:\Program Files\Notepad++\notepad++.exe
Admin mode : OFF
Local Conf mode : OFF
OS Name : Microsoft Windows XP (32-bit)
OS Build : 2600.0
Current ANSI codepage : 1251
Plugins : none