Yeah, that sort of stuff can happen--though it isn't common.
When USPS started "simplifying" their routing in Montana in 2020, after the present Postmaster General was appointed. One thing that happened is that instead of sending mail directly to the town it was addressed to it was first sent to one of the bigger POs first, then rerouted.
For our little the big PO is Great Falls, which is a 130-mile drive north of us. This resulted in mail addressed to somebody HERE going up to GF and back--and sometimes it got routed oddly even in those trips.
Right after that change we had a party for a number of local friends, and sent out invitations a couple weeks in advance. But one invitation got rerouted from GF, and didn't show up until AFTER the party. We asked the local PO if there was some ways around that, and they said yeah, just tell us you want it delivered directly.
This "simplifying" was supposedly done to save money and time, per the Postmaster General's orders. I am guessing that's why your birthday card took so long to show up. (The other invitations to our party all showed up on time.)
We mail a BUNCH of packages each year. One of the problem post offices we've encountered is Denver, which we've started calling "the Denver vortex." On a few occasions our book packages have ended up in Denver for 2-4 weeks, according to the tracking--and a lot of them go through Denver, because it's the biggest PO in the region. But another one that has also "caught and held" packages is Philadelphia, though not as many of our packages go through there.
