in some conditions, while writing text messages, some in combination with phrases such as “IN”, “UN” and the like, typing will crashes and then restarts the device
in other circumstances, however, stop typing, and even though I continued to type in the letters, these were not implemented by the system and therefore not written
After numerous tests, requests for support in the Microsoft Answers Forum for Windows Phone,I found out what was causing the problem:

the grammar proofing
I simply disable the following function by following this path:

Settings> Keyboard> Typing Settings> Keyboard (tap to change)> uncheck Correct misspelled words

Once this is done, the problem is not resubmitted.