My last pen of Lantus did not seem to work, my time in range (using a Libre2 sensor) dramatically reduced from my usual level of 70% to around 40%. Also, my ratios for calculating my Lyumjev (fast acting insulin) changed by a similar proportion. When that Lantus pen was empty & I started a new pen, my time in range went back to previous good levels after a few days. Just wondering if anyone else had experienced this problem? I can't report it to Sanofi as I have disposed of the pen, so don't have a batch number. My insulin is stored in sealed plastic bags at the top of my fridge.