Both these settings show poor stream quality and good preview quality. Video settings are the same:
Preview:

AMD Stream:

Log: https://obsproject.com/logs/XKvSPjuOGFiOT7La
CPU Stream:

Log: https://obsproject.com/logs/JXWF_MFm8okXX60C
FPS is fine, but changing settings doesn't seem to do anything
Soft:
OBS AMD Encoder ver. 2.5.1.0.
AMD Driver ver. 19.1.1
PC:
Ryzen 5 2600X
Sapphire Radeon RX460 4GB
ASUS Prime B350M-E
8GB RAM