If you play with mods I suggest NRaas Overwatch. Overwatch will detect stuck sims and warn you with a notification. By default, Overwatch will automatically reset the sim, but you can change that in it's settings. Once you disable OW from automatically resetting stuck sims you can right click (left click?) on the sim icon in future OW stuck sim notifications and the camera should zoom to the stuck sim. This will allow you to see the problem and determine whether you can fix it.
If the mod zooms you to an inactive's house you can use NRaas MasterController to open the house to see what's going on (click on the walls of the house>NRaas>MasterController>Open). Be sure to use MC to 'close' the house once you are done, otherwise the game will continue to animate the sims on that lot which will affect game performance.
