I've seen this before too, but we did put some recent fixes in UPS (1.2.3) and Keycloak (since 3.4.2) for this.

See:

Please try this setup:
https://github.com/aerogear/aerogear-unifiedpush-server/tree/master/docker-compose/ups-release

If that's still an issue for you, please update here

thanks!