see @neekir there is your problem

your temp limit is 78 (you are already on limit) & you let fan auto speed aka your gpu are already to 77 so is exactly what i think aka you get low hspeed because miner it lower intensity to protect (I/s: = intensity / sec)

try this setting:

- Power Limit 74 = this it suppose to lower heat to a max ~62 my be ~63 depend how is your ambience temp
- set Fan speed to a permanent 65 - 70% (tune your value till you see you get lower temperature) let them work on auto sometime it work badly better keep them on a specific speed always coz your rig is never stop & never rest

idea is to high temperature it lower gpu & miner intensity because it try to self protect so who say keep them on high temp is good tell them to goo to hell .... yes actual gpu can run on high temp BUT that not means it is normal most bad enemies for all electronic is temp & dust
- Temperature limit 80
- Lower GPU clock to 160 that means it will lower temperature to & it will alow to increase memory probabil bigger value but i say agen on equihash speed memory count less

yes hynix is worst vs samsung from any point of view but see what i tell about equihash algoritm ... if you was mining eth i say yup is relevant but in our case nop

the point is you need to get a balance between power usage > temp > fan speed other way you get scrue up your self losing a lot from income & killing your equipment, tuning you can make it with out stop & start miner app if you using windows & msi afterburner but it possible to crash till you find right combo ...

same get a better pool with better latency 250 is bad bad bad special for a dedicate rig

hope it help