When using animation layers on controls with proxy attrs the connection between the proxy attr and the host node will be broken.
Steps to recreate:
I’m pretty sure this is a Maya bug of sorts, but I wanted to know if there is a good work around.
Hey. I’ve had that error on non mGear rigs too. Pretty sure it’s a Maya bug.
Sounds like they fixed this in 2019.
“Animation layers break with proxy attributes MAYA-77709”
yep it is fixed 
We are probably stuck on Maya 2018.5 for the remainder of our film. 
We do NOT use animation layers.
Actually, if an animator updates a rig from foo_v003.ma to foo_v004.ma by just updating the path in the reference editor, proxy attributes are also disconnecting. Sometimes… And sometimes they would magically pop back and start working again once we jiggled the limb a bit… Very strange!
I’m hoping there might be some workarounds or fixes without needing to upgrade Maya yet.
One promising fact, is that if we export the animation using Studio Library, and then reimport it on a fresh rig, it seems to not lose any of the animation. The keyframe info still exists.
yep, same situation here with 2018.5. No proxy channels for us
Hey Chris, Just a heads up; be careful with broken proxy attributes and Studio Library.
It can sometimes save a proxy key/value set to 0, while the key/value of the host control is properly saved. When SL applies the animation/pose to a clean rig it sometimes applies the broken proxy value after the good host value, thus forcing the host to 0.
This caused enough problems for our animators that we removed proxy attributes all together.
Cool thanks for the warning @Lucas_Brown. Last night I just removed all Proxy Attributes from all modules and POST scripts in our pipeline.
All of our pre-prod animation seems to have survived the transition! 
