So my Gamemaster has a private homebrew item I would like to add to my inventory. 

The problem is that I can not find it when searching on my character. If my gamemaster goes in and search for it he can not find it either. 

The funny thing is that all my other players can find the item. I am the only one with homebrew items in my own campaigns and with the Master subscription

Could it be something that collides with my Master and his Master subscription?

Sharing homebrew doesn't require a subscription. What it does require is the following:

1. The homebrew is in your DMs collection
2. Your character needs to be in a campaign either made by the DM, or with one of the DMs characters
3. Your character needs to have homebrew content enabled

Just in case, “Enabled is red (to the right).

Also is this something you are proficient with or no? If not then make sure to uncheck the Proficient check box when searching for said homebrew item.

Thanks somehow I missed that setting. It was the problem. I was sure I had done that