I had to rebuild (but I kept the existing HDDs) my DYI Truenas system. I had been running version 12.0 but I rebuilt using the latest version (11/27/25). After installing the latest version and successfully logging into the system, I imported my storage pool This seemed successful and it also recognized the dataset that existed on the drives. I created a new account and gave that account permission to use the dataset. I was able to log in using Windows FileExplorer, but it shows the dataset is empty. However, on the dashboard is shows that the pool has data on it. (it shows 9.5% of the size of the pool used). ANY help would be appreciated.
It is proper etiquette to include your complete system configuration when you post a query. Without knowing what your system is and the version of TrueNAS, one can only offer general ideas about the nature of your problem.
It is entirely possible that the owner and group permissions on your data files are not set properly. Changing ownership/permission on a data set does not automatically change ownership/permission on all the data in the sub folders.
When I migrated from Core to Scale, I had to reassign owners and groups to access all my data. In my case, I had been running a lot of things in Core under root - which will not work properly in Scale. The Scale documentation has a good discussion about this and is definitely worth the read.
System:
TrueNAS 25.04.2.6 | Supermicro X9SCM-F | Xeon E3-1240V2
32GB ECC RAM | PNY 120GB SSD for boot
3 WD Red 4TB + 1 HGST Deskstar NAS 4TB in RaidZ2
Toshiba 128GB M.2 SSD