Error Msg:

    PID = 43 SptBpduTx

    Bus Error Exception (data) occurred

A data bus error occurs when a data load or store instruction results in either a parity error or memory access timeout. If the CPU attempts to access a memory location where no hardware is present, the system controller will force a data bus error exception to the CPU. Data bus error exceptions can be caused by a software bug or hardware problems.

Since you are already on 8.6(4)-latest CATOS code for SUP2, you either upgrade it to Native IOS or replace the supervisor (recommended if there has been multiple crash due to same reason).

For more details you might want to open a case with Cisco TAC.

Let me know if this helps