Update 2:
I did a clean install of 6.12.4 and just copied my plus.key and network.cfg from my backup.
The GUI felt much faster, but not so fast as 6.12.3.
After I did some changing in the network settings:
Disable bridging, using bonding since I have multiple interfaces (eth0 and eth1)
Settings > Network Settings > eth0 > Enable Bonding = Yes
Settings > Network Settings > eth0 > Enable Bridging = No
Edit VM Manager to use vhost0.
Docker settings, nSettings > Docker > Host access to custom networks = Enabled
Saved the settings, and back to slow gui again. Take much longer - around 15 seconds to open the Dashboard
So I go back to 6.12.3. That one was working great. With Bridging enable and use of br0.
Never seen any call traces because of this.
Update 1:
I tried again today to upgrade to 6.12.4. Sorry to say, same problem again.
Takes 7 - 11 seconds to open the Dashboard. Can't see anything in the: htop at that time.
Only did an inspection in the browser.
This time I disable autostart of Docker and VM.
Only the array was started.
I don't see any special errors in the syslog either.
Update 3:
Revert back to 6.12.3. Here is the dashboard.