Update not possible and error on the editor field

Hi,
we currently have two problems.
This morning i encountered this error. The editor can be changed and then i can save but my answer to the ticket will not be saved. When i go back into the ticket it shows the new editor but after i start editing it, the ticket goes back to the first editor "IT".

I tried updating but everytime i get this error:


I tried upgrading with two different admins, manually with the tthe new app file and tried the wizard with repair option. Nothing works. I have the version 1.2.3.0 in the app catalog and 2.1.14 on the Helpdesk site.

Hello Fabian! I will send you the update instruction through private message.