Unfortunately, it is not uncommon for the update of the BIOS to cause issues in a NUC's BIOS configuration (including fan speed control programming). In fact, I *always*, *always*, *always* completely reprogram the BIOS configuration after applying a BIOS update. That is, I immediately use F2 to enter BIOS Setup (Visual BIOS) and then F9 to load the BIOS configuration defaults. I then make only the changes to the configuration absolutely necessary for the hardware (boot order, SATA Mode, etc. - and yes, fan speed control programming). Don't forget to save the configuration as you exit Visual BIOS.
I am not a fan of the preset fan speed control programming choices in many of the NUCs, but the KY NUC's is especially poor. Here is my recommended configuration:
Give it a try and see if it helps,