Stuck again, luckily, I wasn't in any production, I only tried to reproduce the problem, and I succeed.
Where can I upload the debug.txt?
I think, there is nothing

00:34:35.799 TOracleQuery $065744A0 Start Query.Execute
This is where I started the query, it is not a difficult select.
00:34:35.751 TOracleQuery SQLForm_1.TestQuery Start Query.Describe
SELECT * FROM atg_berterv_elem_szamitas_mod
Later I added some where clause, and the PL/SQL Developer stopped suddenly
The last few rows are :
00:34:35.713 SQLForm Executing...
00:34:35.728 GotoQueryTab 0
00:34:35.729 GotoQueryTab: QueryTabControlChanging
00:34:35.729 GotoQueryTab: QueryTabControlChange
00:34:35.730 QueryTabControlChange: Grid
00:34:35.730 QueryTabControlChange: Show EditPanel 1
00:34:35.732 QueryTabControlChange: Hide Grids 1
00:34:35.732 QueryTabControlChange: Hide Grids 2
00:34:35.733 QueryTabControlChange: GetTableName
00:34:35.733 QueryTabControlChange: SQLMessage =
00:34:35.734 GotoQueryTab done
00:34:35.734 SQLForm Executing...
00:34:35.738 TSQLThread SQLThread Suspend ended
00:34:35.739 TSQLThread SQLThread runs
00:34:35.739 TSQLThread SQLThread loop start
00:34:35.740 Lock
00:34:35.741 TOracleQuery Query Start Query.Execute
SQL = begin :id := sys.dbms_transaction.local_transaction_id; end;
:ID = Null
00:34:35.742 TOracleQuery Query End
Duration = 0
00:34:35.743 TOracleQuery $06572A80 Start Query.Execute
SQL = select a.n_szamitasmod,a.c_nev1 from
atg_berterv_elem_szamitas_mod a
where 1=2
00:34:35.746 UnLock
00:34:35.747 TOracleQuery $06572A80 End (0 records processed)
Duration = 0
00:34:35.751 TOracleQuery SQLForm_1.TestQuery Start Query.Describe
SQL = SELECT * FROM atg_berterv_elem_szamitas_mod
00:34:35.754 TOracleQuery SQLForm_1.TestQuery End
Duration = 0
00:34:35.755 TSQLThread SQLThread loop end
00:34:35.756 TSQLThread SQLThread loop done
00:34:35.757 TOracleQuery Query Start Query.Execute
SQL = begin :id := sys.dbms_transaction.local_transaction_id; end;
:ID = Null
00:34:35.758 TOracleQuery Query End
Duration = 0
00:34:35.758 TSQLThread SQLThread transaction management done
00:34:35.759 TSQLThread SQLThread Postmessage
00:34:35.760 TSQLThread SQLThread Suspend
00:34:35.760 TSQLForm.ThreadFinished
00:34:35.761 TSQLForm.ThreadFinished: SQLThread.Suspended
00:34:35.761 SQLForm [14:27:37] 0 rows selected in 0,016 seconds||ThreadFinished
00:34:35.763 Lock
00:34:35.764 UnLock
00:34:35.768 TOracleSession $079956A0 Start Session.Commit
00:34:35.769 TOracleSession $079956A0 End
Duration = 0
00:34:35.782 Lock
00:34:35.783 UnLock
00:34:35.784 TOracleQuery Query Start Query.Execute
SQL = begin :id := sys.dbms_transaction.local_transaction_id; end;
:ID = Null
00:34:35.785 TOracleQuery Query End
Duration = 0
00:34:35.786 Lock
00:34:35.790 UnLock
00:34:35.791 NavigationBookmarks.EnableButtons(Rebuild)
00:34:35.792 NavigationBookmarks: Backward=10, Forward=0
00:34:35.792 WindowAllowed(3)
00:34:35.793 WindowAllowed done
00:34:35.793 WindowAllowed(2)
00:34:35.794 WindowAllowed done
00:34:35.795 WindowAllowed(6)
00:34:35.795 WindowAllowed done
00:34:35.796 WindowAllowed(4)
00:34:35.796 WindowAllowed done
00:34:35.797 WindowAllowed(5)
00:34:35.797 WindowAllowed done
00:34:35.799 TOracleQuery $065744A0 Start Query.Execute
SQL = declare
Lines sys.dbms_output.chararr;
begin
:NumLines := 10;
sys.dbms_output.get_lines(lines => Lines, numlines => :NumLines);
if :NumLines > 0 then :Line0 := Lines(1); end if;
if :NumLines > 1 then :Line1 := Lines(2); end if;
if :NumLines > 2 then :Line2 := Lines(3); end if;
if :NumLines > 3 then :Line3 := Lines(4); end if;
if :NumLines > 4 then :Line4 := Lines(5); end if;
if :NumLines > 5 then :Line5 := Lines(6); end if;
if :NumLines > 6 then :Line6 := Lines(7); end if;
if :NumLines > 7 then :Line7 := Lines(8); end if;
if :NumLines > 8 then :Line8 := Lines(9); end if;
if :NumLines > 9 then :Line9 := Lines(10); end if;
end;
:NUMLINES = Null
:LINE0 = Null
:LINE1 = Null
:LINE2 = Null
:LINE3 = Null
:LINE4 = Null
:LINE5 = Null
:LINE6 = Null
:LINE7 = Null
:LINE8 = Null
:LINE9 = Null
00:34:35.800 TOracleQuery $065744A0 End
Duration = 0
00:34:35.804 GotoQueryTab 0
00:34:35.805 GotoQueryTab: QueryTabControlChanging
00:34:35.806 GotoQueryTab: QueryTabControlChange
00:34:35.807 QueryTabControlChange: Grid
00:34:35.808 QueryTabControlChange: Show EditPanel 1
00:34:35.809 QueryTabControlChange: Hide Grids 1
00:34:35.810 QueryTabControlChange: Hide Grids 2
00:34:35.810 QueryTabControlChange: GetTableName
00:34:35.811 QueryTabControlChange: SQLMessage = [14:27:37] 0 rows selected in 0,016 seconds
00:34:35.811 SQLForm [14:27:37] 0 rows selected in 0,016 seconds||QueryTabControlChange
00:34:35.812 GotoQueryTab done
00:34:35.813 Lock
00:34:35.817 UnLock