Well, they should never end up there, and you can still move the attachments back into a normal folder to detach them. You may also detach them from the pie menu (right click on attachment and "Detach"), or from the main menu ("Edit" -> "Detach objects"). But I added the attach/detach entries to Lost And Found items for next release...
They do not bear the same names, but the names are too long to fit the spinner label field, and get truncated... I fixed that for next release.
Cannot reproduce here and not seeing any such warning in the log you provided, meaning I cannot diagnose the issue for sure. It is however probably a network issue in intermittent cases, and a gstreamer media type support issue (missing or incompatible CODEC in gstreamer: try a newer version) in the "always failing cases".
Please provide a matching log and precise repro steps.
Your log shows several warnings indicating mismatches between the viewer and the server inventory:
Clear the viewer inventory viewer cache (from "Advanced" -> "Caches"), and relog.
When encountering AISv3 errors (not seen in your log, but may happen when servers get glitchy or network hiccups), you may also try and disable AIS (using the corresponding toggle in "Advanced" -> "Network").