Created attachment 23084 [details] transfer and not checked out I know why this is happening, but it didn't used to happen in previous versions and is confusing library staff. There is not a 'not checked out' error that accompanies any alert about transferring to holds for items that weren't checked out. In the past just the warning message telling the library what to do appeared.
Created attachment 23085 [details] hold and not checked out
These error messages are not a new thing. In my tests they appear going back at least to 3.8.x. The style has changed a little bit in each version, so it could be things simply look different. I'm closing this bug report because everything works as intended. If this behavior is unwanted an enhancement could be proposed to make it configurable.