The pandemic caused an unexpected sudden increase in demand for shipping services. Any efficient logistic system is going to struggle with that.
I waited a month on my first Amazon order after the shutdowns started, but they recovered within a handful of weeks.
I worked for FedEx a couple of decades ago. I'm well out-of-date, but that kind of business can't just suddenly increase capacity by 50%-100%+ overnight. Labor was hard to come by, and they would need training, and in the case of drivers special licensing and background checks.
Differently-routed packages could be due to mislabeling, torn label, damaged packaging, etc., that requires manual handling. Or maybe it slid out of a sorter and got hidden for a bit.
I've had relatives work for USPS. I'm kind of convinced there has been a continued effort to privatize the USPS via doing everything possible to piss off folks, especially USPS workers. They've pulled some really boneheaded things over the years. I'm not even including any 2020 stories, and we should probably stay well clear of that topic. Or maybe that's just normal bureaucratic stupidity.
Back a couple of decades ago, UPS Logistics and FedEx Logistics were battling it out, but pretty much everyone can do distribution logistics these days. Capacity and cost are the two hard parts when unexpected things happen.
There are two Federal Express companies.
FedEx Purple has all the airplanes and does the absolutely, positively deliveries for a small fortune.
FedEx Green is their ground delivery service. It can be delivered by (1) FedEx company personnel in big markets, (2) Subcontractors with routes in rural markets and (3) United States Postal Service out in the country.
For (2) and (3), service can often be compromised and not be great. They vary.
Again, I'm a couple of decades out of date, but there were many FedEx companies. Off the top of my head instead of going to Wikipedia like I should: red for logistics, silver for internal services, green & purple as you described, Roberts Express trucking which I think became FedEx Custom Logistics? In any case, there were a few different trucking operating companies in the Roadway Package Service acquisition for less-than-truckload and other specialized shipping needs. I understand the originally-nonuniform billing initially was not well-received by customers.
But green and purple are the 'last mile' vehicles you see bringing your packages. And maybe FedEx Home? I think I was always confused about that one. I think that's just green for residential routes.