We’ve seen issues where Plus7 streams encoded with Widevine DRM can fail to decode properly, and may show a gray or black screen of garbage. This is due to a library mismatch of the Widevine libraries.
This can be solved by updating the Widevine binaries in the Kodi ARM library directory, but a simpler solution is to update to a nightly build of Kodi v18 (Leia) until a stable release of Kodi v18 is available in the Google Play Store.
You can find the nightly builds of Kodi v18 at http://mirrors.kodi.tv/nightlies/android/.