ORA-31693 ORA-02354 ORA-01555 errors in export

hello. I got error during export. and my export time passes 20 hours. In past It passes 4-5 hours. Error is

ORA-31693: Table data object "IMS2"."VALUES_F" failed to load/unload and is being skipped due to error:
ORA-02354: error in exporting/importing data
ORA-01555: snapshot too old: rollback segment number 198 with name "_SYSSMU198_3484597550$" too small

what can the mistake be? My undo retention

SQL> show parameter undo

NAME                     TYPE     VALUE
------------------------------------ ----------- ------------------------------
_gc_undo_affinity             boolean     FALSE
temp_undo_enabled             boolean     FALSE
undo_management              string     AUTO
undo_retention                 integer     144000
undo_tablespace              string     UNDOTBS2

I have 2 Undo tablespaces, 250 GB.. and I don't have disk usage problem. I use Oracle 12.0.1.2 and ODA machine with 2 rac node. Thanks