Duplicate form ID errors are typically caused by broken plugins.
A duplicate form ID means two different records in a plugin use the same form ID, which obviously is not possible.
Broken means the data in the plugin is corrupt or somehow wrong and can not be processed by xEdit or DynDOLOD.
A duplicate form ID in a plugin can be removed by loading and saving the plugin in Creation Kit.
If the error occurs in the 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.
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.