Does "LDRD" instruction cause "UNDEFINSTR" error on Cortex-M4?

Dear Experts,

    I'm working on a freertos project which is running at Cortex-M4 and I'm being troubled by a problme - hard fault.

The following is my debugging process:

    I dump the registers in the stack when the hardfault happens.

 [Hard fault handler]
R0 = 0x1d8
R1 = 0x2001091f
R2 = 0x398dcd
R3 = 0x0
R4:0x0
R5:0xe4a0
R6:0x0
R7:0x20010928
R8:0xa5a5a5a5
R9:0xa5a5a5a5
R10:0xa5a5a5a5
R11:0xa5a5a5a5
R12 = 0x0
LR = 0x1ffe1987
PC = 0x1ffe199a
PSR = 0x61000000
- FSR/FAR
BFAR = 0xe000ed38
MMFAR = 0xe000ed34
CFSR = 0x10000
HFSR = 0x40000000
DFSR = 0x0
AFSR = 0x0
- Misc
LR/EXC_RETURN = 0xfffffffd

     From the HFSR and CFSR, I can know that hardfault is caused by the "UNDEFINSTR" error.

And the PC is 0x0x1FFE199A, 

Before executing 0x1FFE199A, the LDRD is executed which is due to one uint64_t variable is used. If I change the variable to uint32_t type and there is no "LDRD" instruction generated, and the programme can run well.

So I suspect, the issue I met is related with the "LDRD", but I don't know the rootcause?

One thing I want to say, the hardfault usually happens after the progaramm running for several hours, sometimes 1 hour, sometimes 5 hours.... 

I'm sure the stack is not fulled and the project is compiled by the arm-none-eabi-gcc（2 018-q4-major）.

Can any one give some suggestions for next setp debug?

Thanks a lot!