For no apparent reason, I have not been able to delete emails in the Junk E-mail folder since two days ago. This has not happened before.
The message cache may be corrupted. You can right-click on the folder and choose Properties > Repair. That will re-sync the folder with the server.
Tried doing that, but received the following error msg.
Close eM Client and run C:\Program Files (x86)\eM Client\ DbRepair.exe
If that doesn’t work, and your account is setup as IMAP or Exchange, you can remove the account from eM Client, then add it again.