it could be that your cables are in bad condition, pinched or bared, or you have put the cables too close to a power source and are getting electromagnetic interference due to cross cutting, Or your Ethernet cable may be over 100M without a repeater. It could be that there is dust in your port on the console or the router. Dust is a fantastic insulter, and can stop a kettle lead from turning on a PC (I have seen this a lot). Could be a damaged ethernet port on either your PS4 or your router. could be the router itself with down level firmware or a busted router. Could also be other applications taking up the bandwidth, or even just the time of day you checked it. It could also be that your ISP was running maintenance in your area. Could be that your router needed a restart. When troubleshooting, its always important to check and re-seat and if nessecary, replace cables with known good test cables. Always check the physical layers of the network first, before digging any deeper