Geo Chart / Filled Map broken for Japan municipality level (2nd level administrative division) since early May

Hello,

We are seeing what appears to be a regression in Looker Studio Geo Chart / Filled Map for Japan.

Issue summary:

  • Prefecture level (1st level administrative division) still works correctly.

  • Municipality level (city / ward / town / village, using 2nd level administrative division) is no longer working properly.

  • This had been working until around April 30, but appears broken since early May.

What we observed:

  • Existing reports that previously displayed municipality-level filled maps correctly are now broken.

  • Newly created charts show the same issue.

  • Reports created by different users are also affected.

  • Table charts using the same data source display the raw values correctly.

  • Heatmaps / other map visualizations still appear to work.

  • Only Geo Chart / Filled Map at municipality level seems affected.

Examples (Japan / Hokkaido):

  • Prefecture level: Hokkaido displays correctly.

  • Municipality level values such as Sapporo, Eniwa, etc. do not render correctly on filled maps.

Data source:

  • Google Sheets (also reproduced across multiple reports)

Question:
Is there a known issue or recent change affecting Japan municipality-level geo mapping in Geo Chart / Filled Map?

Any workaround or ETA for fix would be appreciated.

Thank you.