How does Lucio's wallride work? I'm specifically looking for explanation on how speed mechanics work, on how the speed bonus from wallriding stacks and to what actions will I lose speed? I've tried chaining a few wallrides and they seem to definitely increase the speed boost but if I miss and end up having to do a few hops in between it seems random whether or not I'll go back to the normal speed or still retain most of my speed.
If you go to the wiki page for him and his wall ride you will find the following information:
Lúcio is able to ride along a wall's face until either the wall ends or he jumps off. He also is able to move vertically at an angle as this happens. After initiating the Wall Ride, as long as the jump button is held, Lúcio will remain wall riding. The only things that will affect the trajectory are adjusting Crossfade and releasing the jump button. While riding the wall, his movement speed is increased by 20%.
After releasing from a wall, Lúcio gains a slight burst of speed. He can immediately wall ride into another wall, but he cannot continue to wall ride any wall facing the same direction with the old one, including the original. Lúcio must land on the ground or Wall Ride on a wall facing a different direction to reset this. Curved surfaces is considered changing its direction gradually; it means that Lúcio can indefinitely ride "walls" like Ilios' well and Lijiang Tower's control center wall.
So you are seeing that boost of speed when chaining because of the boost on leaving a wall, and the already 20% boost from being on a wall. You will lose speed if the wall angle is off or you try to go backwards, or miss part of the wall (slip).
In Game Options there is a button to turn on backwards wall riding though. (Holding back and jump).