I had a similar issue. I couldn't get the phone to be recognized on my work PC (using a cable that has always worked) or at home on Mac using Android file transfer and a different cable. What I think happened in my case is that I was connected to my PC in MTP mode then I unselected MTP so that neither MTP nor PTP was selected. That is what was aiming for (I only wanted to charge not connect). Though then when I went to plug in later as described above nothing came up. I looked all over for the USB settings to change it back to MTP but couldn't find it. I am sure it is there somewhere.
Anyways, after rebooting several times with no luck, I went nuclear (factory reset) which did the trick. I am running Shiny 4.4.2 and have had a pretty buggy go of it. I am likely switching ROMs, not that this necessarily has anything to do with it.