ORACLE trigger issue - inserted multiple rows instead of one

ORACLE trigger issue - inserted multiple rows instead of one

I have an After Insert trigger on table A, Which is supposed to this - 1)
After a row is inserted into table A, check some data of new row. 2) If
the conditions are met, it will insert those data into another table B. 3)
for one row inserted into table A, if conditions are met, only one row
will be inserted into table B.
This trigger was working as design without any issues. Suddenly, couple of
days ago, we noticed that for some rows inserted (not ALL) in table A,
this trigger inserted multiple rows in table B. There are no apparent
matching pattern in the rows, for which multiple rows in table B was
inserted. There are no patterns in number of multiple rows either. I mean,
for some rows in table A, 19/20/21 rows and some rows 27/28/30 rows were
inserted into table B.
This problem happened for 2 days. And then this problem just disappeared.
Now, I understand this is not an usual ORACLE issue. My question is, have
any of experienced anything like this? if so, what could be the reason for
this abnormal behavior?