I’m not sure how throwing out mail fits into the QAnon narratives, but yeah, of course the mail slowdown and QAnon were going to run into each other at some point, with fucked-up results. (Though that’s a given - when QAnon believers interact with anything, the results are fucked up.)
I regularly get that with all the delivery companies. Because there are package thefts in my neighborhood, I keep a careful watch on when things are going to be delivered, and it’s not that uncommon for a package to be “out for delivery” for several days. (Or I’ll get an email about a delivery the next day, but at some point on the day, the delivery date suddenly switches to the next week - because the package is actually still in a different state.)