Franchise line chemistry changed

I’m a couple of seasons into franchise mode now. I’ve been trading and signing players that fit with my coaches style and I got it to the point where I had line chemistry of +5, +2, +1, +2 and now mid season my chemistry has change to a +3 on line one and the rest are all at zero. I haven’t changed any coaches or traded for any new players. This has ruined all the work I have done. Is this a glitch or is it designed to work this way with the new real life coaches?