I got a Xiaomi Mi Note Pro with MIUI v8 and Android 7.0, when i use the Lock App service on any app i want to protect, that app becomes only a black screen. This happen since MIUI 7 and android 5.5.
In the past i have sended this “bug” to Avast support but the problem is still present. I don’t know if this happens on other devices but its quite annoying because this is a PRO feature but i cant use it.
Is there a way to fix this? And how have you done it?
First I would recommend you to clear the app data: go to “Android Settings→Applications→Avast Mobile Security→Delete cache and user data”. If it does not help, you can try to reinstall the app. Please let me know, if the problem persists.
Hi Teresa.
The problem still there. I even have reinstalled the rom and then the app but the black screen still there. I guess this maybe is an issue with MIUI based roms. MIUI already have an app lock service built in it, i disabled it to try avast’s and… black screen again.
I am out of ideas. Since i bought avast mobile i wasn’t able to use this feature.
:-\
Hi, we got some advice from the developers: go to Xiaomi security app → Permissions → Other permissions → Avast Mobile Security → Display pop-up window → Accept. It should help 
Hi Teresa
Yes, i got this answer from the support team and it fix the issue. Now i can access my app with no problem. Thank you!