This might be an odd question, but, when an attachment transfers from one personality to another, is it always considered to be in play? or does it technically leave play at some point before transferring to the second personality?
In play transfer.
A topic from AEG's L5R CCG Rules forum, copied for Oracle of the Void from a copy of the forum saved in October 2015, so pages it didn't save are missing. Players' names are left out; the rules officials are named. Rulings are as they stood on these dates; later rulings, the rulebooks and the Rules Archive may differ.
when an attachment transfers from one personality to another, is it always considered to be in play?
Yes, the attachment never leaves play during its transfer. See also the Glossary: "Transferring counts as attaching but not entering play."