While testing on iOS I get this error sometimes when logging out from a site. This already happened before, it doesn't have any impact in the app's behavior, but since now we capture the errors to send them to server the user will see the message that there was an error.

This error is related to side menu, specifically to setTranslateX function. My guess is that the side menu is destroyed while getting closed, and that causes the app to crash sometimes (depends on the speed of $mmSitesManager.logout).