I know what you're expecting. That I used a stock soldermask layer with clearances too fine for the manufacturing process, and JLCPCB simply changed it to make it manufacturable within their listed specifications.
Nope. The soldermask layer I sent has a nice and easy solid polygon covering entire area of a quad flat IC, extending about half a mm beyond the edge of the chip.
I've ordered from them before, done the same thing, and they made it no problem.
This time they changed it without any engineering query. Instead of one large polygon, they made the sodlermask opening as 4 small slits for each row of ICs and a fifth hole for the ground pad. The problems with this are multiple. First off, it doesn't work. When trying to reflow a chip to this board, the soldermask opening ends right at the edge of the chip (if not slightly before!), which doesn't even meet the specification for this part. Datasheet specifies pads to extend 0.3mm beyond the edge of the chip. No matter how I try, a filet does not form to the sidepads. So short of having X-ray inspection, you can't even verify a connection is made. Worse, connections are NOT reliably made. The bottom part of the pads is too small for that to occur, reliably. Especially when there's that extra thickness of coverlay that was added around the ground pad!
This is besides the point that I purposely increased the exposed copper slightly larger than the standard footprint so I could solder these chips with an iron. Even if the altered soldermask worked properly when reflowed, I would not use them. I'd have them remade. But at least I could have verified the board works properly in other regards.
Worst of all, this board was a relatively minor change to a previous board, so I did not order prototype quantity. I ordered a fairly large quantity. And not they're all trash.
Now am I being unreasonable? All I asked was for them to be remade with my soldermask layer, and I would bite these boards and pay again. So what happened?
I spent the next week receiving a free lecture from their engineer as to how he fixed my boards. After that waste of time, I finally received instructions to include instructions next time to use my soldermask layer and include the magic words "I accept all risk of solderbridges and losses caused by soldermask." So I hit reorder, added this message, checked out, and what happens?
I get message that I have to start order process all over from the beginning. Adding more salt, I paid them extra to panelize my board for me. Now I have to put the specs and quantities in all over again, reupload gerber, and pay to panelize my board, again. Good grief. I might as well order from a different manufacturer at this point.
This isn't a "don't use JLCPCB" rant. I was happy with them before. Just a caution that you must apparently add a note to request they actually bother to use the gerber files you sent them, especially the soldermask layer. They have a new engineer there who is very bright and eager to improve your boards without notice, and he will also give you free lectures.