All the current answers to this question are just giving the Proguard rules that worked for them, every fix will be different. First off, confirm it’s a Proguard problem by checking that the classes-proguard directory is somewhere in the error message, something like this: Unable to compute hash of /Users/Documents/projectX/app/build/intermediates/classes-proguard/release/classes.jar
This means it’s caused by an earlier Proguard error so you need to scroll up in the Messages window or Gradle Console window and check what warnings or errors you’re getting. Just as an example, in my current project, Square’s Picasso library is causing the error:
Warning: com.squareup.picasso.OkHttpDownloader: can't find referenced class com.squareup.okhttp.OkHttpClient. I just added -dontwarn com.squareup.okhttp.** to ignore the warnings, and the app still worked as normal.
A lot of the Proguard errors will be warnings about some class so just adding -dontwarn for whatever class is causing it in your project often works.
I know the StackOverflow way is just Google the error message, copy and paste the top answer and hope for the best but here you’ve to understand it a bit and figure out the proguard rules for you!