Max is taking a 5th gearbox this weekend , I think I read a while back that they were concerned about the reliability of the gear box? Something to do with it being part of the rear suspension design being run very low to the ground and being very flat?
Makes sense to change it for Spa if you feel like you'll be able to get the 5 places back.
With the cars being so stiffly sprung and the desire to keep the weight as low as possible, I wouldn't be surprised if the gearbox was taking a fair few whacks off the ground.
Frankly, with the performance disparity between RB and the rest, I believe the standings would still be the same if they gave Max a new gearbox every race. They don't seem to have any genuine competitors.