It will "turbocore" on all cores (ie go up from it's base clock of 3.4 to around 3.5/3.6), but will only "precision boost" on one core (with one thread) up to 3.8 or 3.9 with XFR so what you're describing sounds like normal behavior.
Try running something with cpu affinity set to only use core 0 and see if core 0 precision boosts correctly, if not you may have an incorrect bios setting somewhere
I also have a 1700X. It stays at around 3.4GHz or a little higher when the computer is at idle. It should boost up to around 3.8GHz if you put a load on it.
If your Power Plan option is Balanced or Power Saver you will see this behavior. You can test this by temporarily setting Power Plan to High Performance. Then the CPU should run at around 3.8GHz all the time. AMD even recommends you use the High Performance plan for the Ryzen CPU.