The error message you are seeing indicates that the Unreal Engine Editor encountered an access violation while attempting to read memory at address 0x0000000000000000. This type of error can occur for a variety of reasons, including corrupted memory, invalid pointers, or other issues with memory management.
The best solution is to remove content which you think can cause issues like these. Start by seeing if you can package the game if it only uses a blank level and continue to add on other content to see if there is something specific causing the issue. This could be a plugin or imported content from your PC or the Marketplace.