income messages take a long time, pop up in folder for a glimpse or short time, suddenly the folder is totally empty, all have gone

Hi, very nice of you to listen to my problem. It already startet some days ago when I realised that it took very much time to receive mails, in some the content still kept hidden. To work with the about 60 mails listed in the Income-folder, and select some to read the text I was surprised to realize, that in the next moment the folder was empty, none of the mails could be seen on my Windows laptop. I had to switch to the mail-server with Vodafone to see me mails. This situation occured with all folders on 2 Laptops with Windows 10 and windows 11. What could I do ?