first dont use bios from other brand, just mod your own bios, then should be fine, using polaris bios editor should be easy, and lot of tutorial out there how to modding polaris card memory timing, you should try it for fun

Try these settings which I am using on RX cards:

Core MHz: 1150
Memory MHz: 1900
Core Undervolt: 900
MVDD: 0
MVDDCI: 0
Aggressive Undervolt: ON
Powerstage: 04

If your OS allows advance options then input this command for boosted hash rate:

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I think this will stabilise your Rig more and you won't be having any stales.
This is all about the trial and error when you are customising the whole thing. RX has to be played out pretty well.

Also it would be better to mine other coins, for example, REV [Suspicious link removed]d share acceptance rate with your card.

What miner are you using? try changing to another miner.
If the problem is not in the software or in the speed of the Internet connection, then you need to look for the problem in the hardware.
Your settings are correct, I see no reason to change something here

I'm running higher Cclock and memory clock than yours and I'm not having any invalid shares, watch out for your internet connection, latency is the top reason why invalid shares occurs most time

invalid or stale? is the hashrate reported on the pool significantly less than what it says in your mining software?