The problem is a bug i think.

I use a lot of invisible blocks to stop the player at different areas.

But I also use visible blocks.

If you put the invisible flag on the block then it is not enough.

You must use the none-flag for it. Not both.

The problem is: If you are using first the invisible flag for the block and later the none-flag for it, nothing happens. Also if you uncheck the invisible flag. That happens sometimes and there is no chance to solve that problem. I have tried it a lot of times. So i deleted the blocks and build new ones with the none-flag. Then everything should be fine. Do not use the invisible flag.

But make a backup of your levelfiles before you delete anything.