The solution to this was found in a posting on this forum from Keith Brown (thank you - and I quote from his posting so as to leave the solution to the problem I posted about here) - "there is apparently a design flaw in the Mojave OS. If a window pops up and asks if you want to use the microphone, answering “no” will disconnect all of your audio inputs. Apparently, “microphone” means 'all inputs'. Fortunately, you can switch them on by going to System Preferences/Security and Privacy/Privacy/Microphone and checking the software (Cubase in my case) to allow it to use all inputs." So, I did as Keith suggested, and magically complete functionality is restored to my interface and I can now record again into my DAW without me having to go through the hassle of reverting to the previous MacOS.
I have a Behringer UMC204HD interface, connected to a Mac laptop which is used for recording (CuBASE and ProTools). This has worked flawlessly for several years, but after upgrading to the new MacOS Mojave (10.14) a couple of days ago, the interface has stopped sending audio input signals through the jack socket to the software. The interface is recognised by all of the Mac applications, and it works fine on playback, but it stubbornly refuses to record my audio input into either of the DAWs. Does anyone else please have any positive (or negative) experiences with Behringer interfaces after they have updated to MacOS Mojave please, or any suggestions on how to resolve this. I have obviously made the usual adjustments to ensure that the interface is re-selected by the software and the general Mac audio drivers, and as the playback shows, it does seem to be partly working, except for not sending the audio input from the interface into the recording software. Mac Customer Care say that I should revert back to the previous Mac High Sierra OS, but this is an enormous amount of work, and loses >all< of the content created since the the OS upgrade more than a week ago (i.e. emails, files, folders etc), so I am very reluctant to wipe the disk if a different solution can be found. Many thanks for any helpful suggestions that any of you might kindly be able to share.