Comment 23 for bug 1440032

I also have a TP T450s with a Sierra EM 7345. It appears that this piece of hardware is generally a bit unstable:

http://askubuntu.com/questions/580167/wwan-modem-disabeling-by-itself-ubuntu-14-10-lenovo-t440s-sierra-wireless-em7
https://forums.lenovo.com/t5/ThinkPad-Tablets/Thinkpad-10-EM7345-stops-working/m-p/1742115/highlight/true#M28656

I also experienced the card being or not being available after reboots.

I was successful bringing up the card by unloading and loading the cdc_* kernel modules (if necessary, several times):

    modprobe -r cdc_mbim cdc_ncm cdc_wdm
    modprobe cdc_mbim cdc_ncm cdc_wdm

Very unsatisfying, but at least a way to get it working when needed.

I would still be interesting to see a Ubuntu dev's opinion on this issue, especially as the T450s is a Ubuntu-certified machine.