I've been looking at this error recently:
Apr 25 12:51:08 cloudvirt2001-dev nova-compute[2572868]: 2024-04-25 12:51:08.870 2572868 ERROR ovsdbapp.backend.ovs_idl.transaction [-] OVSDB Error: {"details":"cannot delete QoS row 4f1bdbb2-2063-4789-9603-b53982670743 because of 1 remaining reference(s)","error":"referential integrity violation"}