Winter grease for extreme cold temperatures I'm using a fat bike rear hub (Sun Ringle). It malfunctioned twice in less than a month riding everyday in winter ❄️. It stopped turning at all so I had it serviced but then it stopped again when it got down to -37&deg;C.

I do not know the exact causes other than grease durability of parts etc. Could this because I didn't use a winter-specific grease, or would it be indicative of a manufacturing or quality problem with the hub?
I use Agrinol 158, which works down to -50&deg;C. It's a blue color. It is an automotive lithium-based grease and I do not think it was specifically tested for bicycle applications; however, at -37°C it does not matter really as long as it works for someone. The "NLGI 1;2" on the can refers to the NLGI consistency number  meaning it is a "soft" grease with medium viscosity. Maybe you can find an analog where you are.