Bobby Lashley hasn't yet agreed to the terms of the release WWE sent him. He had been medically cleared to return, but asked to be let go after talking to Johnny Ace. There's some heat on Ace for all the people who've left under his tenure with bad things to say about him.
Lashley was upset about the size of his Mania payoff which was 250,000 dollars because the match brought in big money and he'd heard stories about other wrestlers getting over a million for Mania ME payoffs. A lot of workers felt he was just lucky to be on that spot on the card to begin with at that point of his career though. It also says he was mad that the company supported Michael Hayes, who had issues with Kristal.
The stories about Kristal being upset about potential "racial overtones" in the Edge storyline was likely blown out of proportions, and whether there would have been racial elements to a Edge-Kristal pairing is unknown.
Also, company souces said Lashley had become a PR problem for the company in the sense that local promoters were claiming he was difficult to work with when asked to do PR stuff and promote shows.
His contract is a long term one, so WWE is in a position of power when it comes to Lashley's immediate future. Since he's the one who asked to be released and he had a long term contract, he'll probably have to sit at home and do nothing athletically for a while once he gets his release, which is why some think he may have to consider returning to the company.
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It's great how a new guy who worked 15 minutes actually complained about getting 250 grand.