OSMC doesn’t remember how far along the video was

Used to work but now seems to forget where I was watching. Using the right button to fast forward to same spot often causes it to exit the video

Are you stopping it near the beginning or end of the video? Kodi has a default set percentage at the ends of a video where it doesn’t set a resume point. This can be tweaked with an advancedsettings.xml file if one desired it to act different. If this isn’t the issue you really would have to provide more detail and possibly logs. As is, you have provided very little information, so we don’t even know what device your using or where your source file is coming from.