some reasons and solution
Whenever you attempt to enter the Mission menu from the main menu it hangs on loading.
You unable to use the PAYLOAD screen to customize the aircraft weapons load out or also once you in the aircraft you still can't use the ground crew to customize payload.
Probably you can meet other problems with Mission \ Campaign menu or Mission Editor, for example after DCS World update.
Another problem, when loading DCS it always gets stuck at 55% or 57% and will not finish loading. Freezing at 55% upon DCS startup
To solve this problem you need to Rename the folder MissionEditor to any temp name here:
C:\Users\Your_User_Name\Saved Games\DCS.[ver: openbeta ]\MissionEditor
also the MissionEditor folder can be found by RUN menu
Hit at the same time Win+R and copy-paste this:
Enter - OK and you will find requested folder.
Then start the DCS World again ...
The new MissionEditor folder creates automatically instead renamed folder.
You can save renamed folder just in case and copy these files from old to new folder: