Hi @suncat2000,
Autowiring services based on the types they implement is deprecated since Symfony 3.3 and won't be supported in version 4.0.You should rename (or alias) the "mobile_detect.device_view" service to "SunCat\MobileDetectBundle\Helper\DeviceView" instead.
What do you think to make a new branch 2.X to handle new version of Symfony (>3.4) ?