If that is the case, then try checking the "O:\" drive directly.
There should be a hidden "PoolPart.xxxxx" folder on the drive. This is where the software stores the pooled data, and the data "should" be in the same folder structure under this folder.
If the data is there, then there is something going on here with our software and it's not showing it properly.
However, if the data isn't there, then either the data was deleted by something, or there is a problem with the O:\ drive, (likely when it was moved).
That said, if the file was deleted/lost and it wasn't duplicated, then you may want to run data recovery on the drive, and see if you can recover the data in question.
Specifically, StableBit DrivePool should not delete data from the pool, unless it was deleted ON the pool. If you or software you have running didn't delete the content, then this is likely a problem with the disk itself and not the software.
In fact, when balancing and duplicating data, we use a ".COPYTEMP" extension on the destination file until it's moved/copied over, so that if something does happen (sudden power loss, pressing the reset button, etc), that the data is still intact.