I saw this yesterday when I am trying to update Chrome on Android 5.1.1 too.

Play Store will show Unknown error -505 and the update failed.

I think this is a Play Store issue? Removing WebView component since I saw this for Chrome too.

A quick search in internal indicates -505 means the signing key doesn't match. I am getting this error because of I am using an old test device probably, but don't understand why external people getting this error.

ctzsm@, could you post the spec of the device here? Is it a userdebug build? cc'ing aluo@ and satyavathir@ for test repro.

The device I am testing is Nexus 6, userdebug 5.1.1 LMY49K.

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I see below in the log, full log attached.

D/Finsky  ( 4314): [1] PackageInstallerImpl.cancelSession: Canceling session 199100045 for com.android.chrome
E/Finsky  ( 4314): [1] PackageInstallerImpl.handleCommitCallback: Error -505 while installing com.android.chrome: INSTALL_FAILED_UPDATE_INCOMPATIBLE: Package com.android.chrome signatures do not match the previously installed version; ignoring!

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No longer on the Chrome team, e-mail me @google.com if any attention still required from me here, otherwise good luck!

Try "adb uninstall com.android.chrome" from the command line and then reapplying the update worked. This fixed it for me.