Do the stock units usually last longer than custom units?

My first system was a stock and it lasted almost 5 months, my second system was custom and it barely made it 2 months. It began to shed very early and I need to order a new one already.. Is this normal...? If that's the case I will be going stock units from now on.

I had the same exact rituals, lifestyle and sweating for both the stock and custom. If anybody has this information please share! Thanks!