As the title says, how did I backslide? Did I get bumped somehow? Very confusing...

It could be a number of reasons.

If someone had a WL book on hold & then took it off hold, it would throw off your place in line.

Someone might have received a WL book that was in unpostable condition & since it was received with a problem, that person would automatically go back in line again to have another chance at getting the book.  That would also change your position in line.  It can be frustrating but it does happen.

This happens when another member who was "ahead of you" in line previously  and was taken out of line gets back into line. 

This can happen if a member (or members) ahead of you in the Wish List line:

Put her account on Vacation Hold (and this book was not set to auto-request).  This will temporarily move you up in line for the book, since Vacation wishes not on auto-request are hidden by the Vacation Hold.  When the Vacation Hold ends, the member goes back in line ahead of you.  This is a very common scenario. 

Got offered the book but used the Not Now button - this puts the book back on the Wish List in its previous position, on hold.  If (a variable time later) the member removes the Hold from the Wish, that member will be ahead of you in line.

Put this Wish on individual Hold on the Wish List, and then later unHeld it.

Got an offer of the book, but the sender canceled it (did not mail it).

Got an offer of the book, and the sender mailed it, but the book never arrived and it was declared lost in the Mail

Received a "problem" copy of the book - damaged or wrong, etc.  This will put the member back on the Wish List in his or her previous position.

Please be assured that we would NEVER put another member ahead on the Wish List without good cause--in order to go ahead of others on the Wish List, a member MUST have Wish Listed that item earlier (on an earlier date) than they did.

Thank you. Not quite so confused now. I'm sooo close now...