... absolutely the bridles shrink,,,,, you better believe it. Mine have on my 14m Evo 2017 have,,,,,,,,,annnnnnnnd the surprise is, the thicker lower sections were the worst.
A bit of background,,,,, I used to mostly ride big kites and if it got above mid 20's I'd bring out my Evo. The Evo spent most of its flying time in its upper wind ranges but it wasn't always windy so unfortunately the Evo remained in good nic.
I fell in love with foiling so I started to use my smaller kites a lot more so of course now the bridles were getting worked more and I noticed it felt different. I now essentially only use my 9m Neo and very rarely do I jump back on the 14 Evo but when I do, it kinda feels wrong.
I did some measuring of the bridles and to my surprise, sections of the bridles were indeed shorter,,,, definitely not as advertised on the little tags so I added small bits to make the measurements exact, and I mean exact to what was printed on those tags and the kite performance came back.
So, seeing as you probably use your 12m more often than your other kites, there is a very good chance your bridles have shrunk and it only takes a few mm here and there for you to feel it.
Oh and by the way,,,,,,,, make sure your Y point on your click bar is at the highest position. This position essentially mirrors the standard 5 line bar. Slide the little 'thumb screw eyelet' adjuster to the highest setting on the front lines then trim the back lines accordingly using the spare bits in the pocket of the click bar bag.
I found that the lower the Y, you will change the geometry of how the bridle loads the kite and therefore change its feel..... the lower you go, the longer you will have to compensate the back lines. If you mirror the standard 5 line bar you can't go wrong. The thing is with the 2017 Evo is it doesn't have the different knots to attach to compensate for different bars ie lower Y points. Other model kites such as the Neo or the Rebel for example, have different knots for you to attach too, to compensate for this so therefore you don't have to do the 're-trimming'.
Anyway, good luck and hope this helps.
Cheers for now,
Robbie