I started having the exact same error. I am also a rotational player and after adding an imaginary friend to an household and leave it, i started having this last exception:
<?xml version="1.0" ?><root>
<report><version>2</version><sessionid>7a0e80f9d0e4664692abb94</sessionid><type>desync</type><sku>ea.maxis.sims4_64.15.pc</sku><createtime>2025-11-29 12:42:08</createtime><buildsignature>Local.Unknown.Unknown.1.119.109.1020-1.300.000.226.Release</buildsignature><categoryid>build_buy.py:621</categoryid><desyncid>7a0e80f9d0e4664692abb94</desyncid><systemconfig/><screenshot/><desyncdata>Exception in <function buildbuy_session_end at 0x00007FF4AAD98290>, args: (961542349513818153,), kwargs: {} KeyError('Failed to load Household Inventory for household 1') (KeyError: 'Failed to load Household Inventory for household 1') Traceback (most recent call last): File "T:\InGame\Gameplay\Scripts\Server\routing\__init__.py", line 1151, in c_api_navmesh_fence_callback File "T:\InGame\Gameplay\Scripts\Core\sims4\utils.py", line 183, in wrapper File "T:\InGame\Gameplay\Scripts\Server\build_buy.py", line 1223, in buildbuy_session_end File "T:\InGame\Gameplay\Scripts\Server\imaginary_friends\imaginary_friend_service.py", line 387, in on_build_buy_exit File "T:\InGame\Gameplay\Scripts\Server\build_buy.py", line 621, in object_exists_in_household_inventory KeyError: 'Failed to load Household Inventory for household 1'rtim=0 Client Session Time: 25.15 Num Save Errors: 0 Num Load Errors: 0 Current Game State: 0x96d01090 LoadingScreenActiveFlag: 1 Origin Version: 10,5,96,47512 Modded: True SystemInfo: Windows 11 10.0.26200 GPU: AMD Radeon(TM) Graphics 30.0.13044.14002, GUID: 028DE8AF-BA36-11EF-80BF-806E6F6E6963 </desyncdata></report>
</root>
I tried deleting the imaginary friend, removed the household from the lot and added it again. The error continues. I have mods but tried with no mods in a new and an old save. If i add an imaginary friend the error starts.