No Mails visible in any folder/ hitting "properties " and "repair folder" makes it visible in one folder. Repeating the procedure in another works, but mails disappear in the first one again. Troubleshoot procedures #1,2,3 not working

Opening Thunderbird after Computer restart: -> no messages in any folder visible Hitting Properties and "Repair folder" makes them visible Repeating procedure on another folder works, but the mails in the folder repaired before disappear again I tried the procedures #1,2,3, deleting the MSF Files, always with program restart had no positive results Only POP accounts thank you in advance