NVIDIA TITANs used Micron GDDR5 and GDDR5X memory.
My GDDR5X is Micron as well on Poseidon.
Depend of series.
I remember with some Kepler cards Samsung memory was best, next year people continue with Samsung but Hynix OC Better.
For every generation is different.
NVIDIA RTX Titan have Samsung GDDR6
NVIDIA RTX2080/RTX2080Ti Founders Edition have Micron GDDR6.
I didn't read what was problem with RTX FE cards.