I have a problem with the block editing for v3.0.1.
When adding a new block, whether to an existing grid or a newly created grid, it’ll say, “saved”
And then when I go to the frontpage, it’s the same, without the new block.
Please assist 
Hello leokoo!
First of all clear cart cache and try again.
Probably, block doesn't appear because you don't have the corresponding data in this block.
Try to create a simple html block and see if it works.
Best regards, Alt-team