In order to properly answer this question, the network needs to be better described. PING can tell things about the network, but what it tells depends on the way the devices are connected, where they are pinging to and the configuration of the routers.
Assuming this is a wide area WIFI type connection (which the statement my clients' CPE has connected to the AP) may imply, this most likely means that the client is making heavy use of the available bandwidth. Pings of 10ms with 40ms jitter are not that bad for a public-spectrum WIFI network as you can't control what other parties are doing - but, of-course, this depends somewhat on the speed of the links.
It could reflect a bad cable but this is unlikely (if its a bad cable its still passing traffic, but with degraded performance). It could be a bad signal, but more likely its due to WIFI noise if its on a WIFI network. If its on a WIFI network it could affect other clients - but really anything could because its utlising a limited amount of bandwidth between more users.