Okay, so this is a very, very odd situation. I'm sorry for being vague, but I want to attempt to keep any localization down to a minimum.
In my local area, there have been several people using the markets. Sometime earlier this year, someone decided not to go domestic, went balls-out, and ordered a large amount of something from a suspicious location. The package was searched, and the product was discovered. The buyer received a love letter, and everything was quiet for some time.
Before then, domestic orders that were less subtle and more risky were carried out successfully, and all was good, the problem only arose after a non-domestic order was made. Several months later, market activity in my area arose again, in products that would be near-impossible to discover. This was done successfully a handful of times through multiple parties, until something with the very slight potential of being discovered was attempted. It did not make it successfully.
No love letter was received by that party, and was initially shrugged off as bad luck, though the order was made in a very, very small quantity, and through a very, very well reviewed, trusted vendor. However, without coordination, another order through another party had been made (through the same post office). This order was something that under normal circumstances, would have not been confiscated without some level of extremely bad luck. The package was found and confiscated.
What action needs to be taken by all parties? Is this a scenario that has occurred before? Is this something that needs to be taken into consideration when ordering?
In this scenario, the parties were lucky enough to have communication with one another. This is something that could be occurring on a daily basis without knowledge, and give explanation for several missing, confiscated, and discovered packages using even the best of stealth.
Could post offices be screening packages after finding illicit products en-route to other nearby addresses? This is a terrifying revelation. What are your opinions?
Try to look at it a LEO POV. You mention that the seized packages were both large amounts. They might think that an organization is at work. Asking the postal inspector to pay closer attention is a easy but productive step.
Another idea. You speak of all parties as if they're familiar to you. Possible CI situation as well.
Could be even simpler. First letter was noticed and local postal workers are excited and on alert now catching the second package. Bored ass workers with something to do now.
The least step everyone involved is arranging drops outside of that P.O. Are they getting caught there or the local distribution center is something else to consider. I truly doubt your local is the one. Staff just isn't trained for that.
If laying low is possible, def do that. If it is an organization, reconsider your runners.