Well, since the 'Seamless tiling' option is an option within the individual filter settings, I don't see any big sense in setting it in the current filter settings before opening the built-in library browser.
I still prefer the obsolete built-in library browser method to have a quick overview and download filters instead of the web-based download method.
Anyway, this error does not appear today any more, without having changed anything.
Once and a while I get another error
"Filter download failed. Reason: 'download_server_notify() failed().'."
during downloads using the library browser, but the downloads seem to have been completed before.
For the moment the "get_filter_preview(7617,2) failed" crash does not appear any more.

Thanks / solved.
Plotz