ltm ve network interface driver

Does the BIG-IP VE license support v14? Check the range on the license. Did you re-activate license prior to creating new volume with new code? You should be within the upgrade path (https://my.f5.com/manage/s/article/K13845), however, sometimes it makes sense to a) upgrade to latest version within current major release first and b) perform a smaller step upgrade perhaps using v13 first.

Did you perform any troubleshooting while on the v12 code? You should have been able to use the VMware console to access via virtual terminal. Did you have an F5 support case open to have someone on hand to assist with such issues? Did you try to see why the config wasnt loading --- did you try to run the hidden bigpipe command (not removed, but execution path no longer included) with the load daol params? This does a manual load of the staged new config and will output any errors, which you can then tshoot.