Drag and drop issues (guest to host)

[xerces8foo]

Host: Windows 10 Pro 21H2, Vbox 6.1.38 (the free version, no Extension Pack) , 64 bit, 32 GB RAM
Guest: Windows 7 + Guest Additions v6.1.38 , 64 bit, 2 GB RAM

I can not copy files from Guest to Host.

Copy-paste does not do anything. I can copy/paste text, but files don't work. (not sure if this ever worked, but now I tried it because DnD does not work either).

DnD: If I drag files from guest to host, I get dialog 1 (see below) ... aaaand now it suddenly works. I have no idea why.

What happened before, was, that after dropping (releasing the mouse button) into a local folder on the host, I got a dialog (the usual Explorer one), that I need admin privileges to copy. The file name in the dialog was: AppData
After clicking "continue", a copy dialog appeared, collecting data ("Discovering items..."), apparently from my windows user folder ( C:\C:\Users\username ) and discovering over a gigabyte of files, which I canceled.

I tried this several times, even updated the guest additions from 6.1.36 to 6.1.38 (with reboot of the guest), but it still did not work. Until suddenly it did.

Any idea what is going on?

PS: No screenshot, as the problem disappeared while I was writing this report (before I could make a screenshot).

[mpack]

Copy/paste of files has never worked.