Imprecise bus access fault in Cortex M7

I'm trying to write unit tests for non-executable SRAM. As a step in that process, I try to execute code inside SRAM by putting some Thumb opcodes in RAM and then executing them. The opcodes execute fine if I put a tiny delay (~10 millisecs) before executing them. If I don't put any delay then I get imprecise bus access fault, i.e. there is a hard fault and fault register values are:

HFSR = 0x4000.0000
CFSR = 0x0000.0400

Other things to note are:

- The code runs under RTX.

- I have not set any MPU settings. If I'm correct, the defaults allow RWX access to privileged mode. All my code runs in privileged mode.

- The same code runs without any faults on Cortex M4

Any pointers about how to investigate this further will be very helpful.

Thanks!