Clear Command cause code for normal Clear always sends uninitialized cause == 0 which is GSM0808_CAUSE_RADIO_INTERFACE_MESSAGE_FAILURE
A particular problem is determining which BSSMAP Clear Command cause code indicates a perfectly normal clear after all transactions are done.
RR defines a GSM48_RR_CAUSE_NORMAL, but BSSMAP doesn't define such a "normal" cause.
In 3GPP TS 48.008 the chapter for this situation does not indicate any cause code that should be used (188.8.131.52 "Release Due To Transaction Completion").
184.108.40.206 CLEAR COMMAND says:
Typical Cause values are: - call control; - O and M intervention; - equipment failure; - requested terrestrial resource unavailable; - handover successful; - protocol error between BSS and MSC.
"call control" is mentioned in relation to uplink release and to the BSS requesting a clear.
"O and M intervention" is for Operation and Maintenance, does not apply.
"handover successful" is about handover.
All others are error codes and don't qualify for a normal release.
My conclusion is that "call control" is the normal cause code to send for a Clear Command, even if the transactions were not related to voice calls.