USB-C to Ethernet adapter (470-ABND) no longer works with MAC address passthrough

Very disappointed with Dell support: for years, I've been using these "USB-C to Ethernet (PXE Boot)" adapters (model# DBQBCBC064, Dell part 470-ABND) in several Precision machines (models 5510, 5520, 5530, 5540 and 5550), and they worked just fine on Linux (even better than on Windows; no manual driver installation required) with MAC address passthrough.

Now, starting last year, I received a batch of these adapters which simply does not work with MAC address passthrough: the LEDs light up, but because there is some MAC address filtering (company policy), these adapters' MAC addresses are not recognized, and thus they are useless.

I noticed that the labels in the "old" batch are markedly different from the new batch. Here's what the labels look like in both versions ("green tick" is one of the old adapters, which works, while "red X" comes from the new batch, which doesn't work):

The "Model" is exactly the same in both cases, but we see the label has Chinese characters in the new batch, while the old batch didn't have them. I've tried with multiple laptops, I've updated the BIOS, tried several adapters, etc. The behavior is always the same: an adapter from the new batch, in a Linux machine, does not have MAC address passthrough. If I replace it with an old adapter, it works just fine. If I put the new adapter again, it no longer works.

So, there has clearly been some manufacturing difference between them, but it's impossible to know before buying, since it's the same part number! I have been buying the old adapters since 2016 (since they became necessary with the 5510, which has no Ethernet ports), and they always worked on Linux, and with the MAC passthrough. Now, I cannot order them anymore, since they simply don't work.

But what is really appalling is that, after contacting several people in Dell commercial support, technical support, etc (including by e-mail and by phone), they have never acknowledged it, apologized for it, offered any solutions, anything. They don't want to replace them, they don't even admit it is an issue ("it works on Windows, so why should we care?"). They don't consider it as a defective batch; they probably just cheaped out on some component, or messed something up, and found a fix for Windows (I've had to update Windows drivers to make these work on the same laptops which had no issues with the previous models).

I'm trying to stall buying Dell laptops as much as I can for my company, since support has clearly shown that they don't care the least. Is it a "niche" usage? Likely: Linux + MAC address filtering is rare on large companies; but the issue is that, because they don't even admit there is an issue, they will probably never fix it, and it will keep not working with newer laptops (which is already the case).

The least I can do is name and shame them, hoping that at least someone will stop buying Dell laptops until they fix such issues. And if you happen to be in the same situation, good luck: I hope your adapters will work.