I’ve seen 1 of 3 things happen. I’ve seen players accept the deal, I’ve seen players reject the deal and I’ve seen players reject the deal but once you do move to the next week, you no longer see them on the contract screen and they ended up accepting the deal even though it said rejected. Kenny Golladay mysteriously accepted my deal the next week and I’ve seen this “glitch” twice.
I’ve also been successful leaving David Bakatari as a fullback week 17 when I’ve already claimed 1st seed and was able to sign him to a long term deal after the game at a lower price even though his negotiation window opened mid season. I haven’t done testing like you guys do but it may be another option.