I have an Audio A6 2017 2.0 premium. I bought it brand new.I have been using the USB ports as well as as SD slots for music listening. About a year ago I started noticing that the system was not reading all the MP3s in my USB port. I have over 12,800 songs in about 930 folders occupying 51 GB (please, no lectures about better organizing my music). The USB was working fine until one day I noticed that several of the folders seemed empty. The message the panel was giving me was "The directory contains no playable files". I checked on my laptop (Windows 10) and they were there and playable. All MP3s. I tried recopying, formatting the USB drive and copying them again, new USB drives, and even different formatting types (all the ones that are valid for this model per the manual). Nothing worked. I then decided to use the SD Card Reader slots with a 128 GB card. That worked perfectly well. But now over the last couple of weeks I AGAIN have the same problem with the SD card! After it hits the first folder that has that problem, all the subsequent ones in alphabetical order have the same problem. And I used both SD slots and had the same problem.
The problem starts around folder number 826 after reading 11,826 songs. But as I said, I originally did not have this problem with the USB ports and when it started happening I switched to the SD card slots but then it manifested itself again.
Any suggestions/ideas?

Thanks!