Since the error is not so clearly on why this is happening this is where one needs to see whats the actual metadata for the object that is getting deployed .
There is an environment variable in the DX CLI named SFDX_MDAPI_TEMP_DIR you might want to set it to a temp metadata directory so that when sfdx push command runs you see the actual metadata thats being deployed .
Enable in MAC (For windows similar to any other environment variables you set one) using export SFDX_MDAPI_TEMP_DIR=/users/myName/myDXProject/metadata .This assumes you have myDXProject as project folder and metadata as the temporary folder .
Examining the metadata folder will tell whats going on here since it is weird .