As you are running NRaas SP, you can always run an Accounting Report under SP > Household Options. An inheritance would show up there under sources of income. But that's not the first thing I thought of.
There is a bug in the game that has been there since forever whereby a vehicle is sold and the active household gets credit for the sale even though they never owned it in the first place. A specific even amount such as §19,000 tends to match that of a vehicle in the Build/Buy catalog. I don't know how to prevent that from happening, if that's what it is, but I just MC cheat the extra funds away whenever I notice it.
