As of December 2017, Google does not accept the use of Accessibility services for anything except helping people with disabilities. This means that Keepass2Android can no longer provide the accessibility service based AutoFill feature. Otherwise, Google would remove Keepass2Android from Play Store.
If you want to continue using this feature, please install the Accessibility service based AutoFill plugin.
After installation, please enable the accessibility service “KP2A AutoFillPlugin” in the Android system settings. When trying to use the plugin for the first time, KP2A will ask you if the plugin may access the Keepass database. Please accept this to use the plugin.