I have some problem with encrypt

I Have a problem . When I choose encrypt sync.
I set a master password and then joplin auto create a key for encryption. I can enable the new key, but the new key is not in use .
I can not use the new key for encryption , and I can not delete the old key.
When I start sync, I get a error like

Error: Could not encrypt item 90169c3efbcf4a2eb01dfab24e640e4e: Master key is not loaded: 51f99b9a023d44488e1c16b4633b51f2

Can anyone tell me how to delete the old key and use new key to encryption.