Tone Mapping in Resolve
Below are some steps that you can take when working with embedded metadata from video essence files, such as an IMF or mezzanine as your source material.
Steps to take
Anytime a Dolby Vision master is put into the timeline, you should either choose 'Tone Mapping using embedded metadata' or 'Tone Mapping using imported metadata'
Every time you add an edit on the mezzanine/IMF, the L1 mapping option will need to be re-selected for those new elements on the timeline.
Make sure the Dolby Vision project setting is set exactly the same as the metadata embedded in the mezzanine/IMF (CM version, master display, etc.). Otherwise, the mapping could be incorrect and thusly fail.