I lose my world sometimes when i save and quit

i have lost the World i was playing on for atleast 5 times now when i saved and quited my World i actualy almost have stopped playing minecraft singel player due to me don't wanting to los any more Worlds i don't know if the bug came on the new update since i used to play on bedrock edition and just recently for about a month ago bough minecraft java edition do i first started experiencing this bug when the new nether update came.