After migration to 26.2.4 there is a quite frequently (at least once a day for 1500 login attempts)  ERROR: duplicate key value violates unique constraint "constraint_offl_us_ses_pk2"

Note that we have 2 keycloak instances targeting the same DB but when the error occur there is no switching from 1 server to another (all the logs are from the same instance).
The DB is postgresql 15.10. The KC_CACHE is set to ispn and KC_CACHE_STACK to jdbc-ping.
I tried to reproduce manually to find some patterns but could not.
Note that the error occurs on a realm where all the clients are SAML clients from other realms. The login flow just redirects to an external IDP.

related upstream issue is https://github.com/keycloak/keycloak/issues/40374