There are a few things I wanted to share with anyone suffering from these random sentiments.
- If you notice a negative interaction / negative sentiment immediately after it occurs, click on the sim who who gained the sentiment and look for an "apology" interaction. One of my toddlers recently gained a negative sentiment and when I had the parent do the "apology", the sentiment disappeared. I've only had this happen once so I'm not sure if it was a fluke but it's worth mentioning.
- The "hug lovingly" interaction diminishes the hurt sentiment. When sims are talking, you can see their sentiments in a type of drop down menu within the conversation interface at the top middle of the screen. I noticed my toddler's hurt sentiment had the down-arrow minimizations after the "hug lovingly" interaction. I haven't noticed any other interactions causing this minimization yet but I'll keep looking.
- [Edit / Update: I'm now fairly certain that this cheat was enabled by one of the mods I use, which I'm not allowed to mention here. This cheat does not appear when I remove that mod from my game] There is now a built-in cheat to remove all sentiments. If you don't mind cheating to get rid of sentiments, all you need to do is open the cheat console and type testing cheats on, then shift click on the sim with the negative sentiment and look for the "remove all sentiments" options. Note: This will remove all sentiments from the sim on which you shift+click, including any positive sentiments. I don't know when this cheat was added to the shift-click menu, but a good many were added at some point recently. Some of them appear to be related to specific packs; like there's a bowling cheat and also a few Batuu ones.
Hope this helps!