I can't tell you what is happening. In the past years I can count on one hand the ones that went down and then got up and ran off. Iver had a few(poor shot placement) that went down and tried to raise up requiring a second shot to take it out of its misery. Also a few that were dead on their feet and ran few yards, some with softballs sized chest exits but they didn't go down first.
My goto. Bullets, 40gr NBT-20 P, 40gr NBT-22-204(my favorite pelt hunting bullet), 52gr Speer HP Varmint, 222 Rem, 223 Rem, 22-250, 5.6x50R, 55gr Buffalo Arms .228 SP- 22 Savage Highpower 55gr NBT- 6x45, 6mm-204. Only two so called splashes with the 52gr Speer but the were 20ft with the 22-250 and they not only blew up the shoulder they pretty much blew up the whole front half of the coyote, they didn't take a step.
So you recovered the coyote that got up and ran, skin them out and see what happened. With those heavies you should be getting exits or they might not be opening and you don't see the exit. Easy enough to tell with a little detective work and a sharp knife.
You might want to give the Sierra 60gr HP a shot or even one of the 80gr SPs, they've been around a long time killing coyotes.