The most normal reason, I find for massive highs are either needle failure or illness, I’ve noticed the “internal” needle on my Novopen 4 sometimes bends over and fails to go into the vial which can cause a pressure issue in the vial and no insulin to get injected. I’ve had this happen with my Lantis pen too so I suspect its a general problem with the needles. So ensure you change the needle before treating the high 
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