Message : Error issuing app only token; ServiceName *_sharepoint_com_sites_ipmcomdocs;

Hi  @K2Developer-1 ,

This sounds like an Authorization Issue with K2 App O365 which in summary it would seem the issue is that the K2 app is not trusted and you have to re-trust this app.
To do so:

• Go to K2 Management -> OAuth -> Tokens


• Delete the old authorisation tokens.


• After that you have run registration wizard and during this process you create new app OAuth token and the issue should disappear

There were a few older resources as well that you could take a look at:

Is this error only showing when you try activate the K2 for Sharepoint app? 
If so this might be of use, there is a post about Changing from Delegated Permissions to Application Permissions for manually-configured AAD integration which you can do alternatively and then 

Additionally according to Mike's Blog:

"This error can be caused by different reasons. One example is when you still have an old K2 .app file (let’s say from 4.7) whereas you need to use new ones (5.x), when this is the case you need to delete an old app, ensuring that you deleted it also from primary and secondary SharePoint recycle bins."

I would suggest rather logging a ticket with the K2 Support team but either way I hope you come right!