Estou tendo o mesmo problema que este tópico aqui:
https://cursos.alura.com.br/forum/topico-deploy-no-heroku-erro-no-login-do-usuario-criado-66051
Nos logs do heroku aparece esta mensagem:
2020-07-22T19:31:36.585449+00:00 app[web.1]: at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96)
2020-07-22T19:31:36.585520+00:00 app[web.1]: at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:494)
2020-07-22T19:31:36.585590+00:00 app[web.1]: at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:139)
2020-07-22T19:31:36.585660+00:00 app[web.1]: at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92)
2020-07-22T19:31:36.585729+00:00 app[web.1]: at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:87)
2020-07-22T19:31:36.585798+00:00 app[web.1]: at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:343)
2020-07-22T19:31:36.585867+00:00 app[web.1]: at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:412)
2020-07-22T19:31:36.585935+00:00 app[web.1]: at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66)
2020-07-22T19:31:36.593464+00:00 app[web.1]: at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:754)
2020-07-22T19:31:36.593734+00:00 app[web.1]: at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1385)
2020-07-22T19:31:36.593802+00:00 app[web.1]: at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
2020-07-22T19:31:36.594101+00:00 app[web.1]: at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
2020-07-22T19:31:36.594435+00:00 app[web.1]: at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
2020-07-22T19:31:36.599451+00:00 app[web.1]: at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
2020-07-22T19:31:36.599535+00:00 app[web.1]: at java.lang.Thread.run(Thread.java:748)
2020-07-22T19:31:36.600169+00:00 app[web.1]: Caused by: org.hibernate.id.IdentifierGenerationException: ids for this class must be manually assigned before calling save(): br.com.casadocodigo.loja.models.Role