You are probably expecting too much from your extruder. My Hemera’s start to struggle with a 0.6mm nozzle near 40mm/s (somewhere near that). The Titan is lower 35mm/s (?) (24mm/s max extruder speed and even then it barely has enough power to push it through). The bondtech site should have all these numbers for you. I am confident you can not retract at 40mm/s.
I think a 0.8mm nozzle needs to be fed somewhere around 5x the material of a 0.4mm (Pi R^2) so imagine printing at 30mm/s with a 0.4mm nozzle vs 150mm/s. My quick math suggests that is the equivalent of what you are shooting to do.