I have a blackwood a5 with android v6.0 and had the same problem. I installed the app with the unlocker and the widget pack then rebooted the phone and off it all was... I realized that not only the reboot did harm to the installation but it was also not possible to install any widgets before the reboot - they just disappeared immediately from the launcher screen. so I checked the app control in settings but all permissions were o.k. as a next step I transfered the app and all plug-ins (widgets) and the unlocker from the external to the internal system memory. I have installed a sd card as system direct memory but it is of course not internal but still treated as external system memory. so I have put Poweramp from external to internal system memory. to make a long story short: this did the trick! I first checked by installing a widget which then stayed on the screen, then I rebooted and everything was still around with all settings fine. I would be interested if this helps others as well and what explanation the develper team has to this behavior..? good luck!