I have been scratching my head over this all morning, turns out the problem was my own doing.
I entered some incorrect apn credentials on a wp77xx running Legato 19.04.0.
cm data auth chap user@host password
Requesting a data connection with ‘cm data connect’ would return LE_FAULT immediately and within 30 seconds or so the device will reset.
From my end this problem is reproducible using stock firmware - both release 9.1 and 11.