you could try a hard reset , that is factory resetting your phone. Many a times this could solve such issues that you may face on insiders. Furthermore if the issue still persist i would strongly suggest you to roll back to the public version of windows 10 which is much more stable and reliable than the fast ring insiders.
As you mentioned that you feel "disappointed since this is a premium phone" , let me correct you there as your phone is meant to perform its best on the publicly available software and not the one that Microsoft releases to insiders , though there is no harm in doing that but insider builds are half cooked or incomplete and can leave you with multiple bugs and no solution at times. I believe you understood clearly what you are stepping into before joining the insiders and you can never judge the performance of a device running an incomplete software.
You can always roll back to public version using windows device recovery tool , for complete instructions on how to please follow the instructions here :
How to roll back Windows 10 Mobile from Fast and Slow Ring to Production release | Windows Central