Its a fresh installation with latest “current” seafile version.
Just for documentation:
This command will find most filenames that are invalid on windows (run in the folder you are interested in).
find . -name '*[<>:"/\|?* ]*'
Even if you are not using windows it might make sense to correct the paths.
Unfortunately this is still there. Makes it incompatible with Google Drive and Mac and Linux. This got 5k views which is a lot more than most topics. Seems to be a common pain point.
Which version do you use? With correct versions you can check the option to not notify about such errors. This is necessary for some users since they use multiple OS.