When migrating Teams with On Demand Migration (ODM), you may experience the following error in the Event log:
Teams migration error, "Cannot migrate attachment /General/ExampleFile.txt: file not found"
There are two steps in the ODM Teams migration:
First, ODM migrates all of the files that are associated with the Team from the source SharePoint Online site to the target SharePoint Online site. ODM does not currently migrate items from the source recycle bin.
Second, ODM migrates Teams conversations and maps/attaches migrated files back into the target Team conversations. In this case, since the files were not migrated, due to being in the recycle bin, the Teams migration reports the error indicating that the file was not found in the target SharePoint Online site when trying to attach the file to a conversation.
WORKAROUND
Restore all items from the source SharePoint recycle bin prior to the migration, so that the files will be migrated.
