Height limit and bedrock level shifted

Updated to bedrock version 1.17.30. I loaded into one of my superflat worlds and everything was gone except for the tops of some towers that I built. Not even the ground was appearing. Then I realized that the bedrock level had changed. Level 0 is where bedrock spawns and you can't build under it. But level 0 is now where level 40 used to be. So now everything under that is gone. Is this fixable? Please help.