UniFi switches on firmware 7.2.123: SFP+ optics and DACs flap, STP flapping alerts, ports need reboot or forced 1G

After UniFi Network 10.0.140 / switch firmware 7.2.123 several operators saw SFP+ ports (UI optics, UACC-OM-MM-10G-D, MikroTik XS+DA0001 DACs, UACC-CM-RJ45-MG copper modules) flapping on US-XG-16, USW Pro Max, UDM Pro and USW-24-Pro units, with STP State Flapping alerts, ports blocked, and switches needing a power cycle; some links only stayed stable when locked to 1G, and LAG/LACP uplinks were worst. UDM Pro logs showed the SFP state machine cycling between AL_ETH_LM_MODE_10G_OPTIC and DISCONNECTED with sfp-handler Tx Fault (rising) and unplugged from eth10 events for a UACC-CM-RJ45-MG that was physically plugged in. Ubiquiti-brandde modules were reported as the flakiest.

• Hardware: Ubiquiti US-XG-16, Ubiquiti USW Pro Max 16 PoE, Ubiquiti UDM Pro, Ubiquiti UDM Pro Max, Ubiquiti USW-24-Pro, MikroTik CCR1009
• Transceivers: Ubiquiti UACC-OM-MM-10G-D, Ubiquiti UACC-CM-RJ45-MG, MikroTik XS+DA0001 DAC, Ubiquiti UC-DAC-SFP+
• Form factor: SFP+, DAC

Symptoms / messagse:

STP State Flapping
sfp-handler: SFP: eth10 Tx Fault (rising)
New SFP mode detected AL_ETH_LM_MODE_10G_OPTIC -> AL_ETH_LM_MODE_DISCONNECTED
port blocked / switch lock-up