Network issues with sql server
[Can't add comments yet so "commenting" here and a moderator can change it to a comment.]

I would recommend checking the network adapter properties on all systems involved and disabling auto-detect network speed/duplex.  If it's set to auto-detect and you don't want to change it without knowing it's causing a problem, copy some large files and see if you're getting the expected throughput.  If not, auto-detect has probably not negotiated the correct speed an duplex and this will cause poor throughput and flaky connections.  I used to do tech support for a data replication co. and we fixed so many connection stability and throughput issues with this it's not even funny.