Ok, so you have had the grinder for 5 months and you have " cleaned it many times "
How many times is that? and have you taken it apart each time?
A suck out with a vacuum every now and then is all that is really needed and maybe once every 6 months take it apart.
From the pictures it looks to me like you have cleaned the thread too well in the past? removing the grease / lubricant that would have been put there in the factory, which if so needs to be re - lubricated.