Designers changing mockups and calling correct & completed work defects

The business analysts write the ACs with generic "should match the approved mockups", we do the work, sometimes within the same sprint the designers edit the mockups subtlety (add a space, change a font size, change a few letters etc.) and then when the work is being tested, a defect always comes up. Sometimes this is months later and randomly we will have a regression in many spots. Normally it isn't that bad & only noticeable differences between the mockups got reported, however, recently the design team has started reporting defects related to pixel differences in spacing... I've asked the business analysts to include a picture of the mockup in the ticket to avoid these problems & the design team threw a fit saying it's better to use their mockup in live figma because it's more up to date.... I have caught the design team doing this & had a sc of my own when the tester reported a defect & the designers tried to play it off like we were both confused when confronted.

I have two issues with this... Firstly, can they really call it a defect if the spacing size differs slightly between the mockup and the actual page but the style is identical ? If it is being used consistently, I don't see how its a defect. The ACs don't say that it should be to the pixel of the mockup, but it should look like & follow the mockup's design... There is no ACs specifically calling out the margins and padding between elements to the pixel, so adding a defect seems ridiculous. Secondly, and maybe worse... using a live figma board to base the ACs off allows the designers to escape accountability. Any time the designers make a mistake, they can just edit the figma & their mistake turns into the developers mistake adding way more points to stories than would have been if they actually paid attention to the designs. It's so ridiculous that they can change the design mid sprint or sprints later & then call the closed out & completed work a defect, but when their design isn't followed by to the pixel, they have the audacity to open a defect. I'm talking they go into the HTML and then use that as a bases for a defect, if you looked at the mockup it would be identical!

Thoughts?