KMail shows no mails and constantly crashes since KDE Neon upgrade

[Stephan Olbrich]

Hi!

Since I upgraded to KDE Neon, KMail shows no mails anymore. The folder structure is still there but the message list is empty as well as the message view. In addition I get a lot of crashes of KMail/Kontact and akonadi resources which are caused by a PayloadException like this one: https://bugs.kde.org/show_bug.cgi?id=495446
Any ideas what could be wrong?

Regards
Stephan