I suspect the USPS quality of service has deteriorated recently due to various cutbacks in their funding (I'm guessing that latter part -- but they do keep reducing hours etc.) I had a weird experience, not with plants, but with a heavy box of crystals (minerals, not glass) which I shipped cross country in a prepaid priority package. It was under their weight limit which I had checked in advance, but it was heavy for its size.
It reached its destination but was left unclaimed by the carrier, got sent back to the PO of origin, then RE-sent to the destination, where it finally made its way to the address on the label. Looked like it had been kicked around quite a lot despite big red "fragile" stamps all over.
I was just glad it made it finally; I'd given up. I tried once to file a claim on an insured package and though I've forgotten the details, I did learn it wasn't worth the effort to go through all the song and dance.
Too bad. The Postal service used to be a darn good service, IMO. Now, I'm just glad to still have it!