There are three distinct issues that alternate whenever you use the "Create copy from current image" option in the file menus.

1. Krita crashes, either immediately after you select the "Create copy from current image" option, or immediately after the copy has been created and you try to do anything else in krita. Multiple runtime error popup messages appear and won't close. Krita has to be force closed from the task manager.
2. The canvas is copied correctly, but the contents are copied to a fraction of the size of the original, and aligned with the top left corner onto a canvas that's the size of the original document
3. The whole document is copied correctly, but the canvas appears blank until you change the visibility of one of the layers. After you do so, everything appears normal.

All three of these seem to randomly alternate with each other every time you try to copy a document.

Reproducible: Sometimes

Steps to Reproduce:
1. Open a non-blank document
2. Select the "Create copy from current image" option within the file menu

Actual Results:  
Any of the following three outcomes:
1. Krita crashes. Multiple runtime error popups appear and cannot be closed. Krita has to be force closed from the task manager.
2. A document is created with the same canvas dimensions as the original, but the contents are scaled down to a fraction of the original size
3. A correct copy of the document is created, but appears blank until you change the visibility of any layer

Expected Results:  
An exact copy of the document is made without issues

The specific 3.0 beta build I'm using is git d330a4a