Sounds like one of crappy new GPUs...ordinary/good RX560s should have default mem clock 1750MHz, not 1500MHz
Is it "Sapphire Radeon RX Pulse 550 Graphics Card 4GB", 11268-15-20G, any better?
Specifications
Mfr Part Number: 11268-15-20G
Chipset: AMD Radeon RX 550
Boost Engine Clock: 1071 MHz
Video Memory: 4GB GDDR5
Memory Clock: 1500 MHz, 6000 MHz Effective
Memory Interface: 128-bit
Bus: PCI-Express 3.0 x16
Stream Processors: 640
RAMDAC: 400 MHz
Max. Resolution: 5120 x 2880, Support 3x Display Monitors
Connectors: DVI-D, HDMI, DisplayPort
Thermal: Fansink