I think this is very probably it. For those scattered blocks where there are 3 sats/vByte transactions or even lower, there's a huge jump to the next category of fees, often something like 16 or so.

So it makes perfect sense that the big mining pools are including these, because these transactions are their own. But they won't include anyone else's transactions.

Hopefully Sunday morning (when fees are often low) it'll get pushed through. Otherwise I'll need to figure out the whole CPFP - child pays for parent idea. It looks really complicated.