Updated Troubleshooting (markdown)

Troubleshooting.md

@@ -4,6 +4,7 @@
 | Crash / Guru Meditation.                            | Try [Full reset](Completely-reset). If still does not work, try [Updating the Xilinx CPLD on hackrf board](Updating-the-Xilinx-CPLD-on-hackrf-board). If nothing works, [report an issue on GitHub](https://github.com/portapack-mayhem/mayhem-firmware/issues/new/choose). |
 | No splash screen / No time & date / Touchscreen does not work / Status bar icon disappeared / Backlight timeout abnormal / Encoder dial abnormal | Check [settings](https://github.com/portapack-mayhem/mayhem-firmware/wiki/Settings).                                                               |
 | It says xxx missing / can't find xxx / xxx read error / xxx is outdated or you can't see xxx.                     | Make sure sdcard contents matches your [firmware version](https://github.com/portapack-mayhem/mayhem-firmware/releases). |
+| Apps are missing or greyed out after upgrading.  | Make sure sdcard contents matches your [firmware version](https://github.com/portapack-mayhem/mayhem-firmware/releases), particularly the external APPS folder. |
 | Unexpected spike on my waterfall / IQ / spectrum. | It's either a [DC offset](https://hackrf.readthedocs.io/en/latest/faq.html#what-is-the-big-spike-in-the-center-of-my-received-spectrum) or noise from power. For reducing the noise, try using the internal battery. For DC offset, there's nothing you can do. |
 | My computer can't see my HackRF no matter what I do | Try at least 5 different cables. If you are on Windows, try to install [Zadig](https://zadig.akeo.ie/), if not working, try on a Linux machine (exclude Ubuntu) |
 | My sound board app can't see the files i putted in, but my fileman app can | folow [Soundboard](https://github.com/portapack-mayhem/mayhem-firmware/wiki/Soundboard) to make correct file |