Just to be sure I understand, you are using a deployment server? And you have an app, maybe like a "dummy" app, that you use to push splunk restarts to your forwarders? But now that's not working?
If that's the case, is the app and all of the forwarders still associated with a server class? Are the forwarders still checking in, and downloading other app changes? Are you actually making changes to the contents of restart app before saving it? If the contents haven't changed, then maybe splunk thinks no changes need downloaded, and therefore no restart is necessary.
Also, maybe the splunk version of your ds and forwarders could be helpful (maybe there's a known bug). And of course, if anything changed in your env between when it did work and now, that would be good to know.