I posted this in the Facebook page, but I'll post it here as well in case anyone has similar issues.
I am running a custom CR10S setup and the EZBoard Lite. I have a genuine E3D hot end with a 5015 fan. I installed the TH3D Unified Firmware.
The main issue I ran into is that my part cooling fan was not holding the speed at what I had set in my slicer, no matter what I printed. This issue also happened when I manually set the fan speed and the hot end was on. After troubleshooting and chatting with Griffin, I dug into the configuration_adv.h and noticed a feature that was turned on: ADAPTIVE_FAN_SLOWING.
Once I disabled this feature, my fan issue went away. I don't think this feature is quite ready for prime time yet, it appears to be something relatively new in Marlin.
I think this issue was triggered because my hot end still needs PID tuned. My heater cartridge does fine keeping up when the part fan is blowing- so the ADAPTIVE_FAN_SLOWING algorithm was apparently false triggering. BUT I am seeing temp swings of +/- 3 degrees in either direction, whether the part cooling fan is on or not (before PID tuning). It sounds like the intention is to slow the part cooling fan down so the heater cartridge can keep up. Honestly, I'm not sure if it would be better to have your hot end cool down, or your fan to stop blowing. It might be a good idea to surface this setting into the Unified Firmware configuration.h file so users can easily disable it. My recommendation would be to disable it for now anyway. I could see this causing problems on machines like mine that haven't been properly PID tuned.
On a related note, you may want to add a feature to the menu to allow PID tuning, or add that to instructions in the firmware. It seems like the standard pids are not a good fit for my machine anymore out of the box. Chatting with Griffin, it sounds like this is because the MOSFETS on the board may be a little beefier than the standard, so a good PID tune is almost required. Maybe you could set some better default PIDS based on testing machines as well.