The class org.camunda.bpm.engine.impl.persistence.deploy.DeploymentCache caches deployed resources (BPMN, CMMN, DMN models) and can be accessed by multiple threads in parallel. Internally it uses HashMaps. HashMaps are not thread-safe (e.g. chance for infinite loops when putting in parallel, see http://javaeesupportpatterns.blogspot.de/2012/08/java-7-hashmap-vs-concurrenthashmap.html).
Probability of problem occurrence: very low (apparently no user ever had one so far, at least we did not notice)
Worst-case damage: rather high (users might violate SLAs they give to the users of their process applications)