Hashrate is very unstable, going up and down from 15 to 29 MH/s.

Applied default patch using Polaris 1.6.7, no overclock.
When I replace Sapphire with any other brand I have - problem disappears and hashrate is stable at ~29MH/s.
So I assume the problem is with the card brand itself (as I have two of those and they behave identically).

PN: 299-1E387-0008A
SKU#: 11265-05

Thoughts?

Performance graph: https://i.imgur.com/UUeL8iX.png
Model: https://i.imgur.com/IPDPGjt.jpg
Actual card: https://i.imgur.com/KCbDQci.jpg