High number of undistributed commands after a "An existing connection was forcibly closed by the remote host" event
It's almost certainly a network/connectivity issue, even if the jobs don't fail at the same time. 

Error 14152 is logged when "Agent shuts down after unsuccessfully retrying an operation (agent encounters an error such as server not available, deadlock, connection failure, or time-out failure).", and if the last error was "existing connection was forcibly closed" that suggests there were also earlier tries with the same result even if not logged.

There are many reasons this could be happening intermittently. One specific reason can be multiple NICs in the distributor having the same IP assigned. It could also be the network connection is simply overloaded at times.