I play rotationally, and merge households quite frequently.
A "Solution" I have encountered for this problem is to rely on trial and error. I noticed that whenever this error happens, sometimes I can still play with other households. And every time that I can, I'm also able to go back to manage world, and try again to play with the household I merged, and so far, it always works (as long as I can join and play with any household, the error goes away for all of them).
Sometimes, however, I try other households, and get the error on every single one of them. So the only way is to load a save and try again. If I save at this state, that gameplay is essentially corrupt and damaged beyond repair*, so I never save before I know I can join a household. It gets at this stage (one where I can't play with any households) usually when I merge multiple households. The more I merge, the higher the probability I can't play with it.
So, whenever I'm merging households, I save before hand, do the test, ensuring I can join both the "other household" and if so, the "original household that I merged with some household" and if so, usually that save is ok.
I have been doing this for a while (over a month now) and haven't experienced any corruption, say, wrong or missing data, so it's working for me. But I can't vouch that this is a reliable strategy long term for everyone, or even myself, hence me keeping backup saves where I haven't done this.
*one thing I haven't tried much yet, which may work, is creating a new household, just so that the error goes away. The little I have tried doing that, it has worked. Maybe that's something people can try to do in order to recover their saves too.
Worth mentioning, I never merge in live mode. Always at manage world.
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That being said, I don't know if the nature of the error I'm getting, despite having the same code, is the same for everyone else.
I also used quotes when referring to this as a "Solution" because, like I said, I neither know if this is affecting my saves in an unpredictable way that I haven't discovered yet, or that it will work for others. So proceed with backups, caution and at your own risk. Ideally, a solution will come from EA figuring out what's wrong. But for those that can't stand this anymore, this is perhaps a possible method.
