Network device not always renamed

I try to name 3 network interfaces:
- lan for accessing network
- ecat0/ecat1 is fieldbus and should not be configured by the system

I've setup udev rules that names the devices, but the rule seems subject to racecondition with NetworkManager. The problem seems to be that NetworkManager grabs and ups the devices before udev had a chance to rename them. The journal contains the following errors:

Feb 18 12:57:47 testpc systemd-udevd[329]: error changing net interface name 'eth1' to 'ecat1': Device or resource busy
Feb 18 12:57:47 testpc systemd-udevd[329]: could not rename interface '3' from 'eth1' to 'ecat1': Device or resource busy

This does not happen on every boot. On other systems, I've not yet seen this problem.

My fix will be to manually order NetworkManager after "udev settle".

But: How are udev and NM supposed to work at all without proper synchronization? Or what did I miss that makes udev rules work together with NM?