Just want to remind that this is still here. Not sure how certain films get into locked mode where you can't edit certain fields?

If a field is locked, it's been locked by a moderator. Either because they checked it themselves, or because users were constantly adding the wrong information in it, etc. Sometimes moderators make mistakes, and they encourage users to make a report when these mistakes are found.

In a section of the contribution bible (https://www.themoviedb.org/bible/general/59f792a29251413e93000001), under "Locked Fields" you will read:

When you stumble upon incorrectly locked data, please use the report button, explain the problem and link us to a proper source if needed.

Be understanding! We do our best, but we are not above making mistakes. :)

Also, at the end of the section on "Content Issue Reports", you will read:

Be patient! We receive a high volume of reports. Getting a reply may take a few weeks or more. You can bump your request after two months.