Hi, with AMD Radeon Software 18.7.1 WMR Portal enter in a crash/restart loop.
Reverting driver to 18.6.1 seems resolve the problem
CPU - Intel i56600k
GPU - AMD Radeon RX Vega 64
OS - Windows 10 Pro 1703 build 17134.167
HMD - Lenovo Explorer
I'm having the same problem and resolved it by rolling back the driver.
CPU - i5-7600k
GPU - AMD Radeon R9 290
OS - Windows 10 Home 10.0.17134 Build 17134
HMD - HP Windows Mixed Reality Headset