Many lines with garbage is written to the Editor.log file after doing ReimportAll. The important thing is that additional Worker process should run before Reimport All. The Worker0 (or more workers) is started when you open a folder with lots of e.g. textures - this worker generates previews.

How can we reproduce it using the example you attached
1 Open attached project (or use any project which has a folder with textures)
2 Open different folders (e.g. Sprites and Resources and their subfolders) - the Worker0 should be started (you can check this by going to the <project folder>/Logs and check that there is a file called "AssetImportWorker0.log")
3 Do Reimport All
4 When Editor is reopened go to Editor.log and see that there are lots of lines with a garbage (or they might be shown as empty lines) close to the end of the file

Expected results: there should not be garbage in the Editor.log

Note: the attached Editor.log file has that garbage in it.