If a Cache.get(...) needs to load an entry from the cache store, it uses the PersistenceUtil.loadAndStoreInDataContainer(...) method.
This method utilizes a DataContainer.compute(...) operation. However, when the data container is backed by a caffeine BoundedLocalCache, the key of the ComputeAction may not be the same as the key from the command, since caffeine wraps keys with an object (e.g. weak reference) which uses the hashCode returned by System.identityHashCode(...). Since loadAndStoreInDataContainer(...) method calls the loadAndCheckExpiration(...) method using the key from the ComputeAction instead of the key from the command, it these instances are not the same, it will fail to locate the entry in the cache store.
While I have yet to successfully create a reproducer, I've verified the situation in the WF testsuite using the following failed assertion: