One hint more.

Start of new process os.scandir() give invalid modification date for file open for writing until external tool is not called (like explorer, touch, etc.).

So (log open for writing and write is done between 1, 2):
1. Run program with os.scandir() -> dir_entry.stat().st_mtime() = t1.
2. Run program with os.scandir() -> dir_entry.stat().st_mtime() = t1.
Modification is stalled.

Another scenario (log open for writing and write is done between 1, 3):
1. Run program with os.scandir() -> dir_entry.stat().st_mtime() = t1.
2. touch -> dir_entry.path
3. Run program with os.scandir() -> dir_entry.stat().st_mtime() = t2.
Modification works.