Dell S5248F-ON to Supermicro XEM-100 over a QSFP28 100G DAC: link up, line protocol down

A QSFP28 100 Gb DAC supplied by Supermicro linked two Dell S5248F-ON (OS10 10.4.3.6) switches fine, but between the Dell and a Supermicro XEM-100 the port showed up, line protocol is down. Multiple FEC and negotiation combinations were tried. The thread received no answers. Hardware involved: Dell S5248F-ON, Supermicro XEM-100, QSFP28 100G DAC (Supermicro).

• Hardware: Dell S5248F-ON, Supermicro XEM-100
• Transceivers: QSFP28 100G DAC (Supermicro)
• Form fcator: QSFP28, DAC

Symptoms / messages:

up, line protocol is down
cross-vendor 100G DAC