hard wired port on dpc... router dropping regularly

Hi,  I have a an xfinity dpc... router with 4 hard wired ethernet ports.   I run a long (~50 ft) ethernet hard wired run to a shed with a netgear splitter where it services a mac, 2 win 10 machines and a print server where i get ~600 meg download.   It has worked reliably for years, although this problem has been seen before by me.   Nothing that I know of has changed but recently if I don't work on any of these machines for 1/2 hour plus, the connection from the netgear splitter just stops working.   I can see it drops because the indicator light on the splitter for the run to the xfinity router just goes blank.  Sometimes I can get it back by power cycling the splitter or plugging and unplugging the xfinity ethernet line.   I thought ethernet activity would keep the line up but today I wrote a powershell script that pinged a server on my work vpn every 30 seconds and I could see that the line just dropped and the ping stopped working, even with a ping every 30 seconds.  wifi connections to my shed are very reliable but much slower.  Any thoughts, it's just wierd because it's so intermittent.   This happened about a year ago and it just went away.   I see something's that say that windows machines have an eco internet mode (it might sleep and that might mess it up) but I would argue the DPC.... is talking to the splitter, not the machine on the splitter.