Mauro Ranallo's initial departure from WWE apparently had more to do with working under Vince McMahon than issues with JBL.
Mauro Ranallo is a beloved figure in not just pro wrestling right now, but combat sport as a whole. Fresh off the back of heading up the announce team for Floyd Mayweather versus Conor McGregor, having Ranallo under the WWE umbrella right now is a real feather in the company's cap. He adds a legitimacy to the product in NXT right now.
For a while there, however, Ranallo parted ways with WWE, and his sudden disappearance from the product brought a lot of controversy along with it. It took a while, but eventually, details came to the surface that Ranallo surrendered his duties as SmackDown Live's lead announcer because of issues with his depression. Not only that, but apparently working alongside JBL tcaused those issues to flare up.
Since then, Ranallo has returned to WWE, but as an NXT announcer rather than on the main roster. First impressions would make you think that was because JBL isn't an announcer on NXT, but according to Wrestling Observer Newsletter, it isn't as simple as that. While on SmackDown Live, Ranallo didn't simply have a problem with JBL, he didn't agree with Vince McMahon's whole mentality and how he runs things. Allegedly one of the agreements currently in place for Ranallo is that he doesn't deal with McMahon, and simply reports to Triple H and Michael Cole.
With JBL announcing that he would be stepping down as an announcer on SmackDown Live last weekend, it was rumored that Ranallo would take his place. Corey Graves was the man who filled that slot instead, and now that makes a lot more sense. If Ranallo really doesn't like the culture that McMahon created in WWE, then simply removing JBL from that environment wouldn't be enough to convince him to take up his previous position on Tuesday nights.
Convincing Ranallo to come back to WWE is a credit to the company. If all of the above is true though, that's a little worrying. The one plus point to take from it is the man who will eventually take the place of Vince McMahon, Triple H, has a much different mentality when it comes to how talent and Superstars should be treated.