Huawei S6700 iStack fails because different transceiver types are mixed on the stacking ports 45-48

A Huawei S6700 iStack did not form because the optical modules on the dedicated stacking ports 45-48 were of different types; the platform requires identical transceivers on those ports. The four ports 45-48 are the fixed stacking ports, and mixing, for example, an SR module on one and an LR module on another kept the stack from establishing, with no obvious error beyond the failed stack.

• Hardware: Huawei S6700
• Transceivers: stacking-port optical modules
• Form factor: SFP+

Symptoms / messages:

iStack does not form
optical module mismatch on ports 45-48