As the jdk.G1HeapRegionTypeChange event is disabled by default, this has probably not yet been seen. But if it is enabled 119943 out of 226379 events are reporting a region type change from Free to Free. The real type change is written at the same time. See the attached snippet.
From Old to Old is also written, but 112 time only.

Start Time From Index Start To Used
18/04/2024, 09:51:11.133 Old 7 0x23C000000 Old 442 KiB
...
18/04/2024, 09:51:11.866 Free 345 0x38E000000 Free 0 B
18/04/2024, 09:51:11.866 Free 345 0x38E000000 Continues Humongous 0 B
...
18/04/2024, 09:51:14.865 Free 345 0x38E000000 Free 0 B