It seems Japan's MILT (Ministry of Information, Land and Transportation) wants to consider "firmware updates" significant change and they would like to approve every time they issue an update. Which does not make sense, as MILT nor Tesla wouldn't know potential bugs or minor changes that are included in the latest build. It's a software. It is tested so it's safe, but small changes always happen and they won't be clearly documented.
Personally I'm not sure why MILT can do such kind of regulation for "non-type approved cars" like Tesla, as it is not type approved, they have no power over it. Even after firmware changes, there's no changes to the test result of "Shaken" - no length / weight changes, no outer modification, no power changes. Just an incremental change in advanced cruise control.
Right now Tesla is asking MILT to approve firmware by firmware, that's why it takes a long time to deliver the latest version. It seems it's approx 1-2 months late.