The problem has already gone in new versions. It may not be very good choice, but it is suggested to upgrade you EasyAR library. If you found too many differences from 3.0, you can try 3.1 and 4.0, which has a similar API design (not identical).
One big improvement of EasyAR Sense 3/4 Unity Plugin is to use Unity rendering pipeline directly to support ALL rendering APIs Unity support. If you keep using older versions, please make sure to read the documents of certain version first, and make sure rendering API are correctly selected (GLES2 for mobile).