It depends on memory manufacturer. It looks like that you have Hynix memory. If it`s so - you ought to downclock memory to -502.
It is Hynix memory. So I guess I'm stuck at 20 MH/sec ? Or should I try a BIOS flash as proposed earlier ?
Follow the suggestion of user mak013, it's weird, but some memories of 1660s need to downclock to gives more hashrate
I did not believe before but it's true
Here's a link to see some users relating:
https://www.reddit.com/r/EtherMining/comments/j4woit/1660_super_hynix_316mhash_eth/I didn't find the thread here, but there's users from here that suffered the same problem with Hynix.
maybe it's something related to memory timings, when you downclock the memory probably have better timings, but this is just a guess.
Try this and post here