I just 'updated' from 7.2.2.33 to 8.1.20 a few days ago and I Seem to be having the same issue, The software will launch and seem to run OK, but when I check it after a few hours, it is just a blank dark grey/black window. More importantly IT STOPS RECORDING, which defeats the purpose of NVR software. What was the fix from Reolink? or do I need to roll back to v7

Ok, I think I was able to block it using Windows firewall.
I created a "New Rule" and the settings I used were:

Rule Type = Custom
This Program path = "%Program Files% (x86)\Reolink Client\Reolink Client.exe"
Protocol type = UDP
Local Port = All Ports
Remote Port = Specific Ports & 2000
Which local IP addresses does this rule apply to? = Any IP address
Which remote IP addresses does this rule apply to? = These IP addresses: & 255.255.255.255
Action = Block the connection
When does this rule apply? = Domain, Private, & Public

The response from Reolink support:

Sorry to keep you waiting so long,
We confirmed with the R&D that this UDP broadcast is from the Reolink Client.
When you running the Reolink client, it will try to find the Reolink Devices on the LAN via that way.
It is normal and you needn't worry.

Sorry to tell you that for now, it cannot be disabled, but I will report your condition to our R&D department.
Sorry for the inconvenience caused.

I just setup the Reolink Client on my server and I started having trouble with an RFID controller on my network. The RFID controller listens for UDP packets on port 2000 and acts on any commands in them, if they have invalid information/commands, it beeps an error code. After starting the Reolink Client, the RFID controller started beeping out error codes about every 5 seconds. I opened Wireshark to investigate, and I see my server sending out a broadcast UDP packet (to 255.255.255.255:2000) containing "aaaa0000" every 5 seconds, if I close the Reolink Client, the packets stop. I've tried unchecking the "Add device automatically" but the packets continue. Is there a way to disable this UDP Broadcast spamming?