The vulnerability description clearly states that the issue lies in the failure to invalidate the cache when a user account is converted to a bot. The provided commit patches consistently show one key change: the addition of a.InvalidateCacheForUser(user.Id) within the ConvertUserToBot method of the App struct, located in server/channels/app/bot.go. This function is directly responsible for the conversion process. Its failure to invalidate the cache before the patch is the root cause of the vulnerability. The login functions are involved in exploiting the vulnerability (by using the stale cache), but the ConvertUserToBot function is where the flawed logic resided. The test cases added in server/channels/api4/user_test.go also confirm that the ConvertUserToBot action is central to reproducing and verifying the fix for this vulnerability.