Cheap grease is in reality nothing but clay.
Under heat clay dries and goes hard.
Either grease daily (keeps the zerk open) or upgrade to a synthetic grease.
The clay based greases are in all practical purposes very effective but in this day and age there is much better.
LOL, I was 'once gifted' an electric grease gun, well I needed a drill to clean it out as the clay based grease was so hard. (must have been stored over the hot water tank) On the plus side I now own a nice powered grease gun for mere cents (plus labor).