I have exactly the same issue with Sapphire Pulse Vega 56. It also reports some
unreasonably high value (something around 3000rpm) as max fans RPM.

I've found this thread
https://www.hwinfo.com/forum/Thread-Solved-SAPPHIRE-PULSE-Radeon%E2%84%A2-RX-Vega56-8G-HBM2-Wrong-FAN-RPM.
Apparently this issue was solved in windows with AMD driver update.