As alluded to by roy, the mini-box doesn't have a hard drive or any recording functionality, this all comes from the master box and is multiroom-streamed.
So if you're seeing problems with recordings on the mini, one of two things is happening..
1: The main box has a problem either with the live channel or recording, and this will be replicable.
2: There's a problem with the mini <--> Hub connection - testing OnDemand on the mini should replicate this.
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