Salvete!
This is a translation related issue. The English ambiguity itself must be solved before being able to translate this sentence into your language. This message comes from Koha inventory tool. You have to see how it works in English.
Frédéric++ Paul Poulain has learnt me English and that didn't even make sense to me! ;)
In Koha inventory tool, you send a list of barcodes. Each item is then handled by Koha. If an item is check out, Koha do a checkin. If the check-in succeed, this message is displayed:
item was on loan. It was returned before marked as seen
How about changing this to "Item was on loan. It was returned to the shelf before being checked in."
If the check-in fails, for whetever reason, Koha displays this:
item was on loan. couldn't be returned.
I don't see any reason why the check-in should fail, but it happens and Koha report it!
"Item is still on loan. Check in has failed." ? Cheers, Brooke