Disappearing blocks

When I try to make a home and then I have to go all the blocks I place are gone and I use wooden planks

I thought I could make a new game for the new update and have a house and stuff

Instead i was constantly getting wood for my house and then when I place them they dissapear

1. Get wood from tree
2. Make into wooden planks
3. Place the wooden planks
4. Exit the game
5. Return
6. The blocks you placed are gone!