I think you need to try turning the power off to both boxes for a couple of minutes and then power back on, if that doesn't fix it try a factory reset. Out of interest what version software are you on, this seems to be a reoccurring problem recently.
Thanks for your post and apologies to hear you are having an issue with your recordings.
From what you have said, the mini box is having trouble communicating with the main box. The box should be set to fast start or active start so the action will wake the main box to start the recording. If it's on Eco mode, this may not work. Give that a try and if it doesn't help then as per roy247, you can perform a reset.
To do this follow these steps: Settings > System> Factory Reset > (at this point you have 2 options)
First option - Keep recordings - Select this one. Just to be clear, this is not a complete factory reset so you won't lose your recordings, however you will need to sign into apps such as Netflix, Prime, iPlayer and ITV Hub again.
Second Option - Format disk (selecting this one will delete everything including recordings, planned recordings and profiles)