What version of CoreElec are you using ?
What version of NF addon ? (should use v.0.15.2)
What version of inputstream.adaptive ? (should use v.2.3.22.2)
What version of inputstream. helper ? (should use v.0.4.2)
All these can influence NF addon behaviour.
With inputstream.helper 0.4.2 you can reinstall WideVine decryption library to see if that will fix your errors…