RN628X V6.10.4 Unresponsive both with usage of SMB Shares as the admin webconsole

Since a couple of days my RN628X is becoming slower and slower and had reached the point that I can't use it any longer. Everything seems to function correctly and I don't see any erorrs, but opening and saving a file on a share on the NAS can take a very long time and sometimes also results in an error due to time-out. The admin console is at that point also very slow and at times the RN628X seems to function normal and then it returns back into a non responsive mode. Like it is extremely busy with something and as such it does not have resources available to open a file or open the admin console. I use the RN628X on my own, I don't have apps installed on it and the unresposiveness is also when the RN628X should be idle (no back-up jobs and now maintenance jobs running on the volume). I have rebooted the RN628X several times, but that does not help. The only thing I do notice now is that the led of the third disk from the top to down (channel 2) is not constantly  shining blue, where the other disks are or are far more blue. The disk itself shows as healthy and in the logs I can't see any difference between this disk compared to the others. All the disks are the same being: HGST Ultrastar He10 10240GB (SKU: 0F27452, HUH721010ALE600). I have updated the firmware about 20 days ago after I first did the same with my back-up RN628X and another RN526X I own so I thought it was safe to start using the V6.10.4 firmware. I am running Widows 10 Pro, which is updated to include all the released updated so far. This is all I can think of to share for you. I hope someone can tell me what to do.