This is a pretty ordinary game. I salvaged a precursor wreck, and it worked perfectly fine. Then I salvaged the wreck of two of my own ships in the same system and it called them an "unknown class" in the event. See
the screenshot which shows all three salvage events.
The function number: not applicable
The complete error text: event log says "Salvage of unknown class completed by …", but this was a wreck of one of my own ships
The window affected: event text
What you were doing at the time: salvaging a wreck
Conventional or TN start: conventional, but I doubt that it matters
Random or Real Stars: real stars
Is your decimal separator a comma? no
Is the bug is easy to reproduce, intermittent or a one-off? Seems easy to reproduce
If this is a long campaign - say 75 years or longer - let me know the length of the campaign as well: 222 years and a few months