Same here.
I never had text message backup turned on, but I was getting a new phone so I turned it on. Left it on WiFi / charger for 3 days in hopes they'd all get backed up.
I got my phone in January.
So I got the new phone in, did a restore from cloud. All pictures, settings, emails, etc restored...but only January - April's text messages restored (it's October now).
I factory reset and tried again, and the same occured...up to the very same text message, but no further.
I'm thinking my phone might've needed more time to back up OR there's only a certain amount of space the 'cloud' can hold. Either way, this is driving me crazy.
I factory reset the new phone again, but have yet to restore it. I have my old phone on WiFi / charging again, in hopes that more of the text messages will be backed up so that I can get a full restore.
Does anyone else have any additional suggestions?