Reasons for I485 getting rejected

[rk2004]

If I-140 is approved and I 485 is pending for more than an year, are there any reasons for I485 to be rejected?
Has this happened before?

 

[saigc]

possible:
mostly due to security reasons or
if the i485 beneficiary has violated his/her visa in anyway in the past or
if the underlying i140 is revoked by uscis due to fraud or
due to medical reasons or
if the beneficiary do not have any employment offer at the time of interview

if its ac21 case then reason may be:
due to new employers inability to pay. this may apply to startups.
new job is not "same or similar" as per labor.
if the new employer is debarred for immigration benefits due to h1 or labor law violations.