Errors to copy a record with an Assertion failure are typically caused by broken plugins.
Broken means the data in the plugin is corrupt or somehow wrong and can not be processed by xEdit/DynDOLOD.
The error is often caused by a broken bashed patch. Use the latest Wrye Bash version from the #wip-builds channel of the Wrye Bash Discord to create the patch or do not use the CELL patcher.
Use xEdit error check to find and fix some errors. Watch this video. This check will find typical errors caused by editing or using the Creation Kit, it does not test for wrong record data caused by bugs in specific Wrye Bash versions.
Look up all the records from the error message by their form ID in xEdit. Typically the error is triggered by the last plugin to overwrite one of the listed records - even if everything appears to look OK on first glace.
If removing a plugin lets the process run through without issues, it means the plugin is broken.
Temporarily disabling plugins is a troubleshooting step and not a fix. Avoiding or silencing an error message does not fix the error.
Ignore advice to only temporarily disable plugins to complete the process or claims that the plugin is fine to use.
Fix the error or permanently remove the broken plugin. Broken plugins should never be used in the game.
It might be possible to fix a broken plugin by loading and saving it with the Creation Kit.