Device log error when using mxconfig
It sounds like you're doing everything correctly in terms of generating a StageNow generated MX XML profile and then deploying it with a SOTI package. I use the same exact method for all of the Zebra device types that I manage and I don't recall ever seeing that error in the log. The only difference that I can think of is that I'm storing the XML files in another directory (/sdcard/manhmx/) but I don't think that would make any difference in outcome.
Actually I just double checked and I am actually seeing the same error messages in the logs as well, despite the configuration being successfully applied. Maybe it's a bug?
Could be then. I also get an error message when I try to turn on watchsettings. I send the command "watchsettings on" and the log says script command not supported by the device (Zebra TC75x). Have you had that happen with any of your Zebra devices?
I actually was going to suggest you try the watchsettings method given the specific use case of setting the screen timeout value. I assumed that you were likely using MX for setting additional configurations that are not even exposed through that method which is why I held off. Either way, for screen timeouts specifically I have used this script for setting screen timeouts and don't recall running into any issues.
writesecuresetting -sys screen_off_timeout 600000
Then again, I traditionally enroll using Android+ and DA mode and if you're on a Nougat TC75x you might be using Android Enterprise and DO mode, which will support a different set of management features.