Hi Stian,
Thanks for your interest in APM!
There were some breaking changes in apm-server between 6.1 and 6.2. It seems your indexes were created with 6.1, which is not compatible with Kibana 6.2.
Since 6.1 was a beta release for us, we don't provide a migration strategy. The easiest solution is to delete your apm* indexes (note: you will lose all apm-related data) - this will cause them to be re-created with the new index mappings, and everything should work from there.
I hope this resolves the issue. Let me know if you have other questions.