It’s possible that your X-Axis might not be sitting level, this will cause recurrent probing fails because even though it looks like everything is behaving as it should your toolhead is never actually making contact with the washer and is instead hovering just above the nozzle. We have a guide that goes over leveling your X-Axis here that you can try: https://ohai.lulzbot.com/project/leveling-x-axis/maintenance-repairs/
In regards to the fan not working, which fan is not coming on that you are concerned about? Your toolhead should have part cooling fans as well as a heatsink fan, the heatsink fan should come on as soon as the printer does but the part cooling fans are controlled by the setting you have setup in your slicer or by independent commands done through your LCD or Cura. From your description it sounds like you may just be looking at the part cooling fans. If this is the front heatsink fan that is behaving this way my first though would be that two of the fan wiring harnesses positions on your RAMBo got flipped when the new RAMBo was installed. If this is your heatsink fan it would help to see some photos of your RAMBo and wiring so I can look it over for anything out of place.