Sims forget already existing relationships

Hello, I have the same problem with my game. I play without mods or custom content. I play with several households in my game (the household I'm currently playing is in my played households, and the others are in the unplayed households in the household manager until I return to them, as I only enable the automatic age adjustment option for played households). I usually spend one or two Sims weeks with a household and then switch to another. When I return to a previously played household, I find that all the relationships have disappeared! This includes landlords with their tenants (with high friendship levels), teenagers (with their high school friends), and sometimes even romantic relationships within a couple! Is there anything that can be done to prevent the game from deleting friendship data after 15 Sims days?