@TECreasey 

First of all: do you see problems using NAS, such as it becomes unavaliable from time to time?

If not, it may be possible your NAS runs in energy efficient ("green") mode, going to sleep when not in use and woken by WoL (Wake-on-LAN) or similar when device wants to connect to it.

To be absolutely sure, spend some time around Deco your NAS is connected to. Check Deco light when you get NAS disconnect notofication - if it goes Red, that means Deco lost connection, if not - NAS might have entered sleep mode.

If these notifications annoy you as false alerts, find in your NAS configuration settings all options for energy efficiency and turn them off. That might help.

That might also cause problems on its own depending on NAS, such as reduced longevity of hard drives, but it all comes to priorities.

@Alexandre., thank you for your response.

I am not sure that any power-saving modes is the answer because sometimes I get Connected and Disconnected notifications within seconds and minutes of each other some times.

I have had a look at my Synology drive and I can see that the HDD is set to Hibernate after 4 hours of inactivity so I have disabled that just in case that is having an issue.

I cannot see any other power saving or eco modes for the drive.

I will monitor it and see how it goes.

The main reason I posted was to maybe ascertain if I need to move my Deco P9 unit closer to the main unit as I wondered if maybe due to the notifications it was due to the unit disconnecting rather than the drive itself.

I haven't had any issues connecting to the drive that I know of.

@TECreasey 

If you are still getting disconnect alerts after you disabled hibernate, enable it back. It is the one that extends life of your NAS hard drives. It is even set too generously: if nobody uses NAS at night and this setting is configurable, consider reducing Hibernate to 2 or 1 hour. 

That is not related to issue you have, and has opposite effect on keeping NAS from disconnects, but it is good file server housekeeping.

Now, back to the topic. In my opinion, moving P9 closer to Main will not change anything, because it seems to me an issue is between NAS and Deco it is connected to. You can prove or disprove it with simple test: connect something else to the same Deco, by Ethernet cable or wirelessly. For example, bring smartphone to that Deco, turn WiFi on smartphone off and on, ensure that smartphone is connected to that same Deco as NAS and leave smartphone near that Deco till you get next disconnect alerts.

If both NAS and smartphone disconnect and reconnect back simultaneously, that may point at P9 losing connection with Main Deco. If NAS disconnects but smartphone does not, obviously that means P9 stays connected to Main Deco.

If P9 firmware allows Web access and you don't mind looking in logs, I can tell you what to look for. Still, after you run that simple test I described you might not need to investigate further, where disconnection happens: between Decos or between NAS and its Deco.

Also, it is a long shot, but I looked at Synology documentation and see a feature named QuickConnect which could be a suspect. Disable it and see if it changes anything. You can enable it back if it does not and you use it.

Model: X60(2.0)

Firmware Version: 1.0.5 Build 20201013 Rel. 64247

I have the same problem.  The Deco sends me push alerts about my synology NAS disconnecting and reconnecting frequently since the firmware upgrade.  Prior to the firmware upgrade, I didn't get any alerts about the NAS disconnecting.

In my case, the NAS is connected to a switch-->switch-->Main Deco.  Other devices on the same switch do not do the same thing.

I thought maybe it was when the DHCP renewed, but changed it to static in the NAS and it still happens.

I didn't get the notifications prior to the Deco firmware update and the NAS can be in use during times when the alerts occur, at different times.  I think it's a false notification occurring in the Deco.

@Alexandre. thank you for a great reply. Such detail!

I have two wired devices connected to the same P9 unit. I have the Synology NAS and an Apple Time Capsule.

I have enabled notifications for the Time Capsule as well and every time the Synology NAS reports a Disconnect so does the Time Capsule.

I went a step further. 

I have hard wired an Internet Connected Radio to the Time Capsule and with Notifications enabled I get three notifications for the Synology NAS, Time Capsule and Radio.

Does this suggest that maybe the P9 Unit is losing connection?

@TECreasey 

You definitely proved it is not NAS that has a problem.

You have multiple devices connected to both Deco ports reporting disconnect and reconnect. So, it must be Deco node.

If not for @mmascari mentioning he has same issue and it appears to be false notification, I would have said it is Deco node hardware issue. 

In any case, only TP-Link Support can sort that out. Definitely something with Deco.

In case you have access to Deco node logs, these are log lines when Deco loses and restores connection:

Mon Nov  2 10:22:12 2020 daemon.notice conn-indicator: Connectivity changed: ONLINE(0x0) -> OFFLINE(0x1)

...

Mon Nov  2 10:22:42 2020 daemon.notice conn-indicator: Connectivity changed: OFFLINE(0x1) -> ONLINE(0x0)

@Alexandre., great ill see if I can get to the logs and if I can see those connection logs perhaps I can go direct to TP-Link support and get advice from them. 

@Alexandre. 

I was sitting next to mine, on a PC connected right next to the NAS hardwired throught the same network switches when it occured and was able to look at the log.

Tue Nov 24 11:35:06 2020 daemon.err client_mgmt: client(XX-XX-XX-XX-XX-XX) not found in arp table disconnect_counter=2

That looks like when the disconnect notice was sent.

A few minutes later this is in the log, showing it connected fine.

Tue Nov 24 11:39:03 2020 daemon.info udhcpd[6977]: fscanf_num:3 device_mac:........

The disconnect and connect app notifications show up a minute apart.  It looks like something between the Deco and the Synology NAS is causing the Deco to drop it from the arp table.  There's other log messages with disconnect_counter less than 2 for other devices.   And a couple of other devices where the counter gets this high.

Whatever it is, it's super obnoxious to get the disconnect and connect notices a minute apart at all times of the day and night.

This might also explain why we have a phone that seems to drop and reconnect often.  Something going on where the Deco is losing track of devices.