We're working on integrated rest functionality built-in in the Modeler. This is still hidden behind a feature flag for internal testing but the handler is always registered. Unfortunately this is conflicting with the rest module from the app store.
The easiest solution would be to let the rest module run on a different path, I'm not sure if this is configurable in the module but if not, it would be easy enough to change in code. Would this be a sufficient workaround for you?
Edit: In 5.14 I changed it so that it doesn't register the handler as long as the feature is not enabled.
This workaround will solve the issue: it changes the default path of the Rest Services module:
(Btw, for those wondering: this Model Share was added to this answer by just pasting the url of the model share page into the question)