I believe I am having a similar issue. I've implemented Global HTTP Proxy on supervised devices (as a test) but something was configured incorrectly. Now, I am unable to send any type of commands to the devices. I would like to remove the profile (really, just update the reset changes to the existing profile). Seemingly, the only way to reset the profile change is to put the iPad in recovery mode. This, however, isn't feasible for elementary students in remote learning. If anyone receives this message, please let me know of a fix. (I am instructional tech for a school, not informational tech so my knowledge is limited.)
