Jon - don't have an answer as such for you... but I do have a few questions, the answers to which might help others give you something better
What version are you on?
Do you use DeepFreeze or similar, for "protecting" your PCs? If so, is the configuration/settings directory for this in an unfrozen area??
We came across the DeepFreeze thing ourselves following a recent upgrade of our environment which added DeepFreeze to the mix, which we'd not "played with" before. The Deployment folks that built the image were not aware that Pharos was "aware" of DeepFreeze, and were also not aware that DeepFreeze needed to have its' config area in a "thawed" zone so that Pharos could update it. That solved a large number of the issues we were experiencing following the rollout of the new machines. One of those issues was very siilar to what you're experiencing - updates being pushed out from the server weren't getting to workstations for some reason, and the only way we were able to get them out was to restart the Pharos services (not a good look, when everyone gets booted off when that happens!)
We have, in the past, had complaints of machines doing what you're reporting here - but I've not had any further reports of it for some time... and I'm not sure if it was the change to the DeepFreeze config which has done it, or if folks have simply not noticed it recently... so I'll definitely be keeping an eye on this one to see how you get on... just in case someone comes up with something I can check to make sure we don't still have an apparently-dormant issue which can still come back to bite us (me!) later.
We are on version 8.3.7184.331 and the machines having the problems do not have DeepFreeze installed. We have machines with DeepFreeze installed and configured correctly. The DeepFreeze machines are not experiencing the problem.
We determined that the issue was caused by bandwidth problems. When we limited wifi access to 1 meg the problems were reduced from about 10 per day to about 3 per week. When the suclientscheduledreservations.bin file is not updated these problems will occur.