Is there a command that the leaves do not disappear?
Try it:
/ gamerule randomTickSpeed 0
Hmm, that's not the true thing
It gives the block state persistent. If you would somehow apply this to all leaves and set it to true, it would not disappear.
Joa… In certain cases (for example, a lobby at a server) despite the very good
Or they were simply placed by hand
When leaves are placed by hand, they disappear the same way. Or did I get it wrong now?
No. There's the block property "persistent". For natural leaves, this is set to "false", for those who have been set by hand, however, it is "true". Therefore, the alternative suggestion to somehow set all sheets to persistent: true.