welcome to the world of downclocking drivers report your specs here and hopefully someday in the far end future we will get updated drivers that will allow our cards to not downclock when we are ingame...
I hear that amd updates driver automatically for 5700xt and thus gpu will not work 100% . This reduces the heat of gpu but make gpu down clock ! . And I hear that you can not reverse this when update automatically new driver ! . So turn off automatically update if possible for the new buyer of this card ! . No thing can be done for you in this situation ! . Maybe in the future , auto update from amd without the permission of end users will be stopped ! . Luck that i have bought yet this desire card . I wait until find to way to turn off automatic update ! .
Looks like there are problems in RX 5000 Series, and the issue still not solved yet. I also have this kind of issue with my RX 5600XT.
You can join here, as the thread got many comments and replied by moderator.