Network Speed on RN102

Hi,

i have been running the NAS RN102 with 2 Western Digital RED Drives 2TB for the past 3 years without any problems. i am also running the latest version of firmware 6.4.2  

recently when i access the NAS device through windows 10 i get a very long lag to a point where sometimes it also times out. i imagined that this might be a network problem and therefor i purchased a NEW router and a NEW Gigabite Switch. i thought this would help but unfortunatly it did not. i tested out the network by transfering files from one pc to another and speed was fine. 

due to this i decided to back up all my NAS and gave it a factory defaults including formatting both drive. when i started transfering the data back i got the same problem where the speed drops to 0 and at some point it peeks at 45MB/s 

the trouble is that when i access the NAS trough computer i still get timeout errors and a slow transfer/connection. 

anyone had any similar problems and how can i resolve this?