Here are the Spec for your Sapphire RX580 Pulse:
Can you clarify exactly how many adapters you have and what type? You should have three adapters, one per monitor.
HDMI-VGA, DP-VGA, and DVI-VGA?
When you have all three monitors connected what does Windows 10 Settings under "Display" show?
Does all three Monitors show up in "Device Manager" under "Monitor"?