I just use the old plastic steering shaft mount on an adjustable bracket with the chain ran thru the hole.Good point .
A simple spring loaded tensioner or guide rail on the bottom chain run .
i use a laserCheck your chain alignment with a flashlight at bottom of chain at rear sprocket entry. Look directly through top part of chain to check entry to sprocket.
2015 kinetic stock axle, no weight jackerAre you running a left rear weight jacker? Cold be pitching axle too much.
What wall thickness of axle are you using? Torque/stall...unloading and loading of axle can be a big issue.
Motor plate flex upon torque loading.
Chassis flex...more common on older 1 1/8” chassis’s.