I recall hearing a few years ago that this in particular was something that Kawhi didn't like (might have even been timvp, RIP, who said this?). Have heard other commentators also mention that what the Spurs did here is a practice that tends to rub players and agents the wrong way (and that is understandable since it adds an element of risk to a player getting an extension that they would rather avoid).
I never thought that this would be *the* thing that caused the split though... wild if so. You'd think that if it's that big of a deal, the player and agent would make it known at the time at which point the team can decide on whether or not that's the star they want to continue to build around or if maybe they should start thinking of other options. At the same time, from an organizational standpoint you sure as shit want to have your star player's blessing before doing this kind of move. That part is so obvious that I'd be shocked if the Spurs didn't think they had Kawhi's blessing. Perhaps Kawhi signed off but because he's unable to use his words to share his feelings he secretly resented the team for it.