I have a program working in the Android Emulator. Every now and again I have been creating a signed .apk and exporting it to my HTC Desire to test. It has all been fine.
I faced a similar issue today and at first i thought it was my sd card which corrupted it. I tried it on many devices running android 4.4 and up but it kept bringing the same issue.After some googling and research i realized that i didn't select the v1 jar signature which is for devices older than android 7.0 nougat so i applied both of these signatures by selecting the two check boxes and generated a signed apk and it worked.
Link to solution Android – App not installed error when installing a signed APK – How to Fix