When an account falls off or is deleted from your credit report the average account age changes. I am thinking that this is what is causing this scenario for you. For example if you has a loan on your report for 10 years and then it falls off this would change the account age in your profile. The fico score takes all the accounts ages combined.
EXAMPLE:
10 YEARS LOAN 10 YEARS CREDIT CARD 30 YEARS ON A MORTGAGE LOAN
IF YOU ADD ALL THREE THE AVERAGE ACCOUNT AGE IS 16.6 YEARS
NOW LET'S SAY THE MORTGAGE LOAN FALLS OFF THE REPORT
10 YEAR LOAN 10 YEAR LOAN
ADD THE TWO LOAN ACCOUNTS TOGETHER THEN DIVIDE BY 2
NOW THE NEW AVERAGE IS 10 YEARS
BY HAVING THE MORTGAGE LAON DELETED YOU KNOW HAVE 6.6 YEARS LESS AND A LOWER AVAERAGE ACCOUNT AGE.
That is why you need to have and hold on to open accounts as long as possible. The best type of acocunst thta you can have are your credit cards.