Lightroom: Importing of new raw files not working properly

Yes,
I knoiw there is a previous post on this matter, but as this problem might have something to do with the iOS i post as new thread.

On iMac running Yosemite LR 5.6 does not see my new raw images (Canon 1Dx), neither from CF-card nor when copied separately into new folder on separate USB3 WDMyBookStudio3TB. i.e. Import procedure fails.

I copied the same RAW files to another folder on the same external HDD, LR sees and imports the files w/o problems. I have seen many other other people suffering from the same problem, I have seen many solution suggestions, I solved the problem by selecting the source to the relevant folder on the top left window of the import screen.

It seems I have to do this for every new import session.
Until yesterday everything was working fine w/o problems, I have done no change to any settings on computer and Lightroom, BUT I have reset the OS because of trouble with a USB port that did not work properly. It seems the USB port problem was fixed, but this new problem with LR appeared instead.
I find the LR problem annoying and troublesome, please let me know if there is any setting somewhere that I should change/reset - maybe this setting was changed by resetting the iOS.

By resetting the iOS I mean the following procedure:
Shut down iMac, disconnect all USB peripherals, unplug the mains cord for 10 minues, reconnect with mains, restart iMac, reconnect each USB device one by one.

Can someone please tell me what actually has happened with LR?

Thank you
Micha