Unity Fails to Build to Android Device - INSTALL_PARSE_FAILED_NOT_APK: Failed to parse. How to solve this?

• Running Unity 2018.3.10f1

• AR Application, Running Vuforia 8.0.10

• Running Google Firebase Auth / Storage for download of Asset Bundles per User

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Until very recently, this app has functioned fine. I have dozens of previous successful APK/OBB duos. Now, since a handful of updates and bug fixes (Firebase to 5.6.0, etc), my export functionality has stalled. Upon an attempt to actually side-load a new APK/OBB onto a device for further testing, I get a Parse Error:

CommandInvokationFailure: Unable to install APK to device. Please make sure the Android SDK is installed and is properly configured in the Editor. See the Console for more details.

Further:

C:\Users[USER]\AppData\Local\Android\sdk\platform-tools\adb.exe -s "HT7530206306" install -r "C:\Users[USER][FILEPATH]\AR View0.8.0.apk"

stderr[ adb: failed to install C:\Users\USER[FILEPATH]\AR View0.8.0.apk:

Failure [INSTALL_PARSE_FAILED_NOT_APK: Failed to parse /data/app/vmdl1540219450.tmp/base.apk]

stdout [Performing Streamed Install]

exit code: 1

At this point I'm lost on what to do. I have:

• Uninstalled/Reinstalled Android Studio

• Updated Unity to Current Version

• Tried this in a BLANK Unity project and gotten the same error

• Made sure that my device (I think?) no longer has any versions of the app present on it.

• Created a new signing certificate and tried both new and old..

What else IS there? Thanks for your help!