Flashback archive query error ora-01555

I'm using Oracle database 18c. I created an FDA with a retention period of 365 days and I associated a table with this FDA:

• When I query the table using "versions between timestamp minvalue and maxvalue", I only get the updates done today.
• If I replace "minvalue" with an actual timestamp, I get all the results correctly.
• If the timestamp is older than a certain date, I get error ora-01555. I couldn't know what is the actual minimum date. Last week it was about a month but today it is only 5 days.
• Today I found that there is nothing in the history! All history data for last week is purged!