SGX is introducing the “Trade at Close” (TAC) session from 3 June 2019.

In preparation for this new implementation, SGX will purge off all unfilled long dated (Good-till-Date, Good-till-Maximum) orders entered prior to 31 May 2019, 5.05pm.
Such orders will have order status reflected as "Expired" on 1 June 2019.

You may wish to keep a record of such long dated orders (shown as "Expired" on 1 June 2019) and re-enter your orders accordingly.