Unresolved form ID errors signify records that try to use non-existing records in the same or master plugins.
This can happen due to outdated plugins or if records being used by other records are removed without taking care of such dependencies.
Start by checking the plugin and record mentioned in the Error in ... message.
In case the message mentions that a plugin might be the wrong version, double check it is the correct version for the game version and for any other plugins using it as a master. For example, do not use plugins or paid mods from the Creation Club Anniversary Edition with outdated vanilla game plugins from before the Anniversary update. Update the required plugins and use matching versions. For example, do not forget to update the cleaned version of Update.esm after game updates.
If unresolved form ID errors happen while modding Skyrim VR - especially when the error mentions Update.esm or DLC might be the wrong version - the error is most likely caused by a plugin that was made for Skyrim or Skyrim Special Edition. Creating a patch with Skyrim VR - USSEP 4.2.2 and SSE 1.5.97 Compatibility Patch to include updates from Skyrim Special Edition should help in those cases.
If unresolved form ID errors happen while modding Enderal or Enderal SE, the error is most likely caused by a plugin that was made for Skyrim or Skyrim Special Edition. Enderal or Enderal SE do not have any data in the DLC plugins and only a rudimentary Update.esm without any of the actual records that exist in the vanilla Update.esm of Skyrim Special Edition. Even the Skyrim.esm from Enderal does not have all the same records as the one from Skyrim. Even worse, a plugin made for Skyrim can overwrite completely different records in Enderal. Plugins depending on records found in vanilla Skyrim plugins need to thoroughly checked, updated and fixed for Enderal in order to work correctly.
In case the unresolved form ID is for a script property and the intended record can not be determined or the property has been removed from the script, remove the property from the properties listing.
If removing a plugin lets the process run through without issues, it means the plugin has errors that need to be fixed.
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 a plugin with errors is OK to be used.
Fix the error or permanently remove the problematic plugin. Such plugins and badly made mods should not be used in the game.
Make use of the official DynDOLOD support forum in case help is required to identify or to fix errors.