After update my dasboard and setting are gone

After an update from 6.0.1. to 8.3.4 all my settings and dashboards are gone.
Is there a way I can get them back?
Hours and hours work gone?
Can someone please tell me what to do.

Regards
Reinier

According to the docs, “Upgrading is generally safe (between many minor and one major version) and dashboards and graphs will look the same.”

It appears you upgraded by 2 major versions (6.x to 8.x). Did you do a backup? If not, then you may have lost your work.