Missing layers when packaging existing QGIS project in QGIS 4.0+

QGIS Version: 4.0.3

Steps to reproduce issue:

• open/ create QGIS project
• tap the "add" button from the Mergin Maps toolbar
• choose "Package current project"
• a window with layers to be packaged will pop up

Expected output:
All the layers from the opened QGIS project should be listed, just like in previous versions, so that a user can choose which one to be packaged.

Actual output:
No layer is shown in the packaging layers list (see image below), thus the user cannot pick the layers to be packaged.

NOTE: Even if the layers do not appear in the packaging list window, if we press 'Next' and follow the next step, the Mergin Maps project is created with all the layers from the initial QGIS project. The bug seems to be occurring for selecting which layers to be packaged or not.

Image:

Reproduce the issue in QGIS 4.0.3 by opening a project and using the Mergin Maps toolbar's “Package current project” flow. Trace the packaging layers list and compare it with the subsequent step, then verify that the existing project's layers appear and can be selected for packaging.