Only latest 5 blocks show in the block element

When i make 5 blocks and place them in the email all is ok. But when I make block 6, go to the email, place an block element on the email, the dropdown in the block element only shows blocks 2 to 6 and if block 1 has been used on that email it disappears. I than made block 7 and repeated above, on the email block 2 had disappeared. I then placed blocks 6 and 7 in the bin and returned to the email, blocks 1 and 2 where back in the email and in the dropdown in the element.

I was thinking maybe there was a limited on the amount of blocks that can be used, but couldn’t find this in the docs.