If they're wired in to a local switch, then it shouldn't be a remote connection then (that uses a VPN to connect). However, thinking about it now, could REALLY long lines be involved? (Beyond the length for the spec of the cable perhaps?)
Was also thinking 40Mb(it) per second didn't really fit any cable. But that was using 60s as an actual base line, to which OP did say 60s+ (plus), meaning it's likely more, but has seen 60s before (as best optimum transfer). So that got me thinking maybe 5 x 20Mb(it) per second connections? Especially if all devices are transferring at the same time to the core system. Which then suggests the swtich might not be a 1Gb(it) switch or has been set to 100Mb(it) rather than run at 1Gb(it).
So many possibilities here, need more info from OP.