If you run the MTBF / MTTR Report and it seems like data is missing, make sure you don't have Dispatch Types configured in such a way that they cancel each other out. Note the "Limited to non-simultaneous Dispatch Types" alert. Make sure you are not inadvertently limiting report results with conflicting setups in Dispatch Types.
Also check to make sure you've included any recently inactivated Machines/Assets as this may impact the returned report results: Include Inactive Lines/Buildings/Machines/Assets
Probably not every Asset/Item/Machine in your facility directly produces the product you manufacture. Nevertheless, support equipment is important and may be critical to your processes. Be certain to check the "Include Non-Production Machines" box, if applicable,as this may drastically skew your report results and is frequently overlooked.